КОНТАКТЫ

Руководитель:

д.ф.-м.н. Терещенко Олег Евгеньевич
телефон: (383) 330-78-83
e-mail:

Адрес:

г. Новосибирск, ул. Пирогова, 30
Термостатированный корпус ИФП СО РАН

СОТРУДНИКИ

Терещенко Олег Евгеньевич
старший научный сотрудник, д.ф.-м.н.
и.о. зав. лабораторией
тел.330-78-83, вн. 1943
+7913-932-1079
414 ТК
Альперович Виталий Львович
главный научный сотрудник, д.ф.-м.н.
тел. 330-98-74, вн. 1989
253 ТК
Дудкина Валентина Вадимовна
техник
тел. 330-88-88, вн. 1998 310 ТК
Арисов Владимир Васильевич
токарь 6р
тел. 330-88-88 011 ТК
Ахундов Игорь Олегович
старший научный сотрудник, к.ф.-м.н.
тел. 330-66-31, вн. 1984
337 ТК
Бакин Василий Вениаминович
младший научный сотрудник
тел. 330-88-08
218 ТК
Верчук Максим Михайлович
студент (рук. – Хорошилов В.С.)
Иваненков Никита Юрьевич
инженер
тел. 330-98-74 013 ТК
Иваненков Юрий Викторович
инженер
тел. 330-98-74 013 ТК
Ищенко Денис Вячеславович
научный сотрудник, к.ф.-м.н.
тел. 330-98-74, вн. 1988
+7983-323-3996
254а ТК
Казанцев Дмитрий Михайлович
научный сотрудник, к.ф.-м.н.
тел. 330-98-74, вн. 1989
253 ТК
Крамер Полина Васильевна
техник
тел. 330-88-88
414 ТК
Кустов Данил Александрович
инженер-исследователь
тел. 330-78-83, вн. 1943
414 ТК
Кырова Екатерина Денисовна
Студент (4 курс, рук. – Ищенко Д.В.)
тел. 330-98-74, вн. 1988
254а ТК
Михеев Сергей Сергеевич
студент (4 курс, рук. – Шайблер Г.Э.)
тел. 330-98-74, вн. 1980 252 ТК
Молодцова Екатерина Леонидовна
ведущий инженер-технолог
тел. 330-66-31
349 ТК
Рожков Станислав Александрович
инженер
тел. 330-98-74, вн.1389
216 ТК
Рудая Нина Сергеевна
ведущий инженер-технолог
тел. 330-98-74, вн.1331, 1334
254 ТК
316 ТК
Степанов Савотей Андреевич
студент (рук. – Бакин В.В.)
тел. 330-88-08 218 ТК
Супрун Сергей Петрович
старший научный сотрудник, к.ф.-м.н.
тел. 330-78-83, вн. 1943
414 ТК
Федосенко Евгений Владимирович
научный сотрудник
тел. 330-88-88, вн. 1218
128 ТК
Хорошилов Владимир Сергеевич
инженер-исследователь
тел. 330-98-74
253 ТК
217 ТК
Шайблер Генрих Эрнстович
старший научный сотрудник, к.ф.-м.н.
тел. 330-98-74, вн. 1980
252 ТК
Шамирзаев Тимур Сезгирович
ведущий научный сотрудник, д.ф.-м.н.
тел. 330-44-75
350а ТК
Эпов Владимир Станиславович
инженер-технолог
тел. 330-66-31, вн. 1984
349 ТК

и.о. заведующего лабораторией
О.Е. Терещенко
д.ф.-м.н.

тел. (383) 330-78-83
E-mail:

ОБЩАЯ ИНФОРМАЦИЯ

Основными направлениями деятельности лаборатории являются:

  • Проведение исследований в области технологии гетероэпитаксиальных структур и изучение их свойств, в том числе структур на основе узкозонных соединений A4B6.

  • Разработка физических основ фоточувствительных устройств на гетероэпитаксиальных структурах.

ПУБЛИКАЦИИ

2023

Аксенов М.С., Голяшов В.А., Терещенко О.Е. Пассивация фтором границы раздела оксид/InAs(001) // Письма в Журнал технической физики. 2023. Т. 49. № 5. С. 6-9. DOI: 10.21883/PJTF.2023.05.54661.19413

Показано, что фторсодержащие анодные слои на поверхности n-InAs(001) в отличие от анодных слоев без фтора формируют границу раздела с открепленным уровнем Ферми, плотность состояний на которой вблизи середины запрещенной зоны составляет ~ 1011 eV-1· cm-2 (78 K). Изучение химического состава показало, что уменьшение плотности состояний связано с образованием оксифторидов индия и мышьяка вблизи границы раздела.

Закиров Е.Р., Кеслер В.Г., Сидоров Г.Ю., Голяшов В.А., Терещенко О.Е., Марин Д.В., Якушев М.В. Жидкостные методы химической обработки поверхности HgCdTe // Журнал структурной химии. 2023. Т. 64. № 3. С. 108216. DOI: 10.26902/JSC_id108216

Предварительная химическая обработка и очистка поверхности - одна из ключевых операций в полупроводниковых технологиях. Развитие методов подготовки поверхности теллурида кадмия-ртути (КРТ, HgCdTe) актуально в связи с широким спектром существующих и потенциальных применений этого материала в фотоэлектронике. С помощью методов РФЭС и АСМ в работе исследовалось влияние различных химических обработок на химический состав и микрорельеф поверхности HgCdTe. Среди всех рассмотренных травителей только водный аммиак эффективно удаляет собственный оксид HgCdTe, не оставляет поверхностного слоя металлического теллура и обеспечивает близкий к стехиометрии химический состав поверхности. Определено оптимальное время обработки в водном аммиаке.

Казанцев Д.М., Хорошилов В.С., Шайблер Г.Э., Альперович В.Л. Перенос электронов через границу полупроводник-вакуум с отрицательным и положительным электронным сродством: влияние скачка массы // Физика твердого тела. 2023. Т. 65. № 8. С. 1271-1280. DOI: 10.21883/FTT.2023.08.56143.130

Рассмотрено влияние скачка массы электрона на границе кристалл-вакуум на фотоэмиссию из полупроводников. В приближении эффективных масс рассчитаны угловые и энергетические зависимости коэффициента прохождения электронов через границы со скачком массы и потенциальными ступеньками различных знаков, соответствующих отрицательному и положительному электронному сродству. Показано, что благодаря скачку массы, существуют критическая энергия и критический угол падения электронов, которые разделяют качественно различные угловые и энергетические зависимости коэффициента прохождения соответственно. Скачок массы делает возможным прохождение электронов (вплоть до полного прохождения) через положительную потенциальную ступеньку при нормальной компоненте кинетической энергии ниже высоты ступеньки. Расчетные зависимости квантового выхода эмиссии термализованных электронов от величины сродства сопоставлены с экспериментальными данными по фотоэмиссии из p-GaAs(Cs,O). Проанализированы возможные причины существенных отличий эксперимента от расчета: сложный ход потенциала, включающий приповерхностный изгиб зон в полупроводнике и потенциал сил заряда-изображения в вакууме, рассеяние в (Cs,O)-слое, а также необходимость выхода за пределы приближения эффективных масс и учета блоховского характера волновых функций в полупроводнике.

Климов А.Э., Ахундов И.О., Голяшов В.А., Горшков Д.В., Ищенко Д.В., Сидоров Г.Ю., Пащин Н.С., Супрун С.П., Тарасов А.С., Федосенко Е.В., Терещенко О.Е. Фоточувствительность полевого транзистора металл-диэлектрик-полупроводник на основе пленки PbSnTe: In с составом вблизи инверсии зон // Письма в Журнал технической физики. 2023. Т. 49. № 3. С. 22-25.

На основе пленки PbSnTe: In/(111)BaF2 впервые создан макет полевого транзистора со структурой металл-диэлектрик-полупроводник (МДП-транзистора) c подзатворным диэлектриком Al2O3. При T=4.2 K под действием затворного напряжения -7.7<Ugate<+7.7 V относительное изменение тока сток-исток Delta Ids/Ids достигало ~ 5 раз. При освещении малыми (~ 100 photon/s) потоками обнаружена отрицательная фотопроводимость с уменьшением Ids до ~ 104 раз с одновременным уменьшением Delta Ids до ~ 103 раз и более. Оценка обнаружительной способности дала ~ 7· 1016 cm· Hz0.5· W-1 на длине волны λ~ 25 μm при времени накопления ~ 0.5 s. Обсуждается качественная модель, предполагающая существование глубоких уровней ловушек и фотоемкостного эффекта.

Хорошилов В.С., Казанцев Д.М., Рожков С.А., Альперович В.Л. Фотоэдс на поверхности сильнолегированного p+-GaAs с адсорбированными слоями цезия и кислорода // Письма в Журнал технической физики. 2023. Т. 49. № 21. С. 24-28. DOI: 10.61011/PJTF.2023.21.56460.19703

Разработана новая методика измерения поверхностной фотоэдс, основанная на зависимости квантового выхода фотоэмиссии от величины изгиба зон. С помощью этой методики изучена эволюция фотоэдс в сильнолегированном p+-GaAs (6·1018 cm-3) при адсорбции цезия и кислорода. Обнаружены обратимые изменения величины фотоэдс, которые качественно отличаются от наблюдавшихся ранее на слаболегированных образцах и объясняются вариациями скорости поверхностной рекомбинации при формировании и распаде двумерных цезиевых кластеров.

Хорошилов В.С., Протопопов Д.Е., Казанцев Д.М., Шайблер Г.Э., Альперович В.Л. Пленение излучения и субзонный пик в спектрах квантового выхода фотоэмиссии из p-GaAs(Cs,O) // Письма в Журнал технической физики. 2023. Т. 49. № 1. С. 23-26. DOI: 10.21883/PJTF.2023.01.54053.19401

В спектрах квантового выхода фотоэмиссии из p-GaAs(Cs,O), измеренных в геометрии "на отражение", обнаружен пик при энергии фотонов, меньшей ширины запрещенной зоны GaAs. Показано, что возникновение пика связано с пленением слабопоглощаемого излучения из-за диффузного рассеяния на шероховатой задней грани эпитаксиальной структуры. Обсуждаются возможные микроскопические механизмы возникновения пика: эффект Франца-Келдыша в поверхностном электрическом поле и модифицированные адсорбцией оптические переходы в адатомах цезия.

Kazantsev D.M., Akhundov I.O., Kozhuhov A.S., Khoroshilov V.S., Shvarts N.L., Alperovich V.L., Latyshev A.V. Kinetically driven thermal roughening of semiconductor surfaces: experiment on GaAs and Monte Carlo simulation // Physica Scripta. 2023. Т. 98. № 3. С. 035702. DOI: 10.1088/1402-4896/acb6bc

We present the results of GaAs annealing experiments in the conditions near equilibrium, which clarify the reasons of the transition from surface smoothing to roughening at temperatures above 650 °C. The roughening is due to kinetic instabilities arising under deviation of annealing conditions towards growth or sublimation. These instabilities reveal themselves in appearing islands (for sublimation) and pits (for growth) of multilayer heights and depths, respectively. The islands and pits appear due to the motion of atomic steps through surface spots, at which sublimation and growth are suppressed. Pinning of the steps at these spots also lead to step bunching at surfaces with sufficiently small terrace widths. This explanation is consistent with Monte Carlo simulations of atomic processes on the GaAs surface. The similarity and distinctions in surface roughening under sublimation and growth, along with the role of Schwöbel barrier, are discussed. Annealing experiments in the cavities, which are formed by GaAs substrates with well-controlled atomic step densities enabled us to clarify the roughening mechanisms and to improve the efficiency of GaAs thermal smoothing technique by increasing smoothing temperature up to 775 °C.

Stepina N.P., Bazhenov A.O., Shumilin A.V., Kuntsevich A.Yu., Kirienko V.V., Zhdanov E.S., Ishchenko D.V., Tereshchenko O.E. Indication for an anomalous magnetoresistance mechanism in (Bi, Sb)2(Te, Se)3 three-dimensional topological insulator thin films // Physical Review B. 2023. Т. 108. № 11. С. 115401. DOI: 10.1103/PhysRevB.108.115401

Electron states with the spin-momentum-locked Dirac dispersion at the surface of a three-dimensional (3D) topological insulator are known to lead to weak antilocalization (WAL), i.e., low temperature and low-magnetic-field quantum interference-induced positive magnetoresistance (MR). In this work, we report on the MR measurements in (Bi,Sb)2(Te,Se)3 3D topological insulator thin films epitaxially grown on Si(111), demonstrating an anomalous WAL amplitude. This anomalously high amplitude of WAL cannot be explained by parabolic or linear MR and indicates the existence of an additional MR mechanism. Another supporting observation is not linear in the classically weak magnetic field Hall effect in the same films. The increase of the low-field Hall coefficient, with respect to the higher-field value, reaches 10%. We consistently explain both transport features within a two-liquid model, where the mobility of one of the components strongly drops in a weak magnetic field. We argue that this dependence may arise from the Zeeman-field-induced gap opening mechanism.

Talochkin A.B., Kokh K.A., Tereshchenko O.E. Optical phonons of GeSbTe alloys: influence of structural disorder // Journal of Alloys and Compounds. 2023. Т. 942. С. 169122. DOI: 10.1016/j.jallcom.2023.169122

Phase-change materials such as pseudobinary GeSbTe (GST) alloys are widely used for fabrication of rewritable and nonvolatile memory devices and also reveal perspective thermoelectric parameters. Their electron spectrum demonstrates the topological insulator behavior. These promising properties are related to unique structural features of a lattice, study of which attracts much attention since full clarity was not achieved so far. Here, we study Raman spectra of monocrystalline GST alloys to examine influence of lattice structure on phonon spectrum. In the Raman spectra, the broad bands typical for the amorphous state and sharp lines of the crystalline one are observed. The use of a one-dimensional harmonic chain model of atoms composing the lattice unit cell allows us to explain the origin of these features. It is shown that the first component is related to dispersion of phonon frequencies in the different lattice unit cells, which is caused by Ge/Sb disorder. The sharp spectral lines are attributed to phonons originated from those of Sb2Te3 as the structural basis of GST. Their frequencies are invariants relative to Ge/Sb disorder, and GST alloy is an ordered crystal for these modes.

2022

Глазкова Д.А., Естюнин Д.А., Климовских И.И., Макарова Т.П., Терещенко О.Е., Кох К.А., Голяшов В.А., Королева А.В., Шикин А.М. Электронная структура магнитных топологических изоляторов серии Mn(Bi1-xSbx)2Te4 при изменении концентрации атомов Sb // Письма в Журнал экспериментальной и теоретической физики. 2022. Т. 115. № 5-6 (3). С. 315-321. DOI: 10.31857/S1234567822050081 (перевод - Glazkova D.A., Estyunin D.A., Klimovskikh I.I., Makarova T.P., Koroleva A.V., Shikin A.M., Tereshchenko O.E., Golyashov V.A., Kokh K.A. Electronic structure of magnetic topological insulators Mn(Bi1-xSbx)2Te4 with various concentration of Sb atoms // JETP Letters. 2022. Т. 115. № 5. С. 286-291. DOI: 10.1134/S0021364022100083)

Собственный магнитный топологический изолятор MnBi2Te4 представляет собой многообещающую платформу для реализации квантового аномального эффекта Холла при повышенных температурах и других уникальных топологических эффектов. Однако для этого запрещенная зона в точке Дирака должна располагаться на уровне Ферми. Одним из широко используемых способов сдвига точки Дирака в область уровня Ферми является частичное замещение атомов Bi атомами Sb. В данной работе представлены результаты исследований электронной структуры остовных уровней и валентной зоны для соединений Mn(Bi1-xSbx)2Te4 при изменении концентрации (x) атомов Sb (от 0 до 1). Показано, что с увеличением концентрации атомов Sb точка Дирака сдвигается в сторону уровня Ферми с локализацией на уровне Ферми при x ≈ 0.3. При этом наблюдается “жесткий” сдвиг валентной зоны, включая уровень Mn 3d, без видимых изменений структуры валентной и зоны проводимости. Концентрационная зависимость сдвига точки Дирака аппроксимируется корневой функцией, что соответствует линейному возрастанию плотности носителей заряда. (Intrinsic magnetic topological insulator MnBi2Te4 provides a promising platform to implement the quantum anomalous Hall effect at increased temperatures and other unique topological effects. However, to do this, the energy gap opening at the Dirac point should be located at the Fermi level. One of the widely used methods to shift the Dirac point toward the Fermi level is the partial substitution of Bi atoms for Sb atoms. In this work, the electronic structure of the core levels and valence band of Mn(Bi1-xSbx)2Te4 compounds with various concentration x of Sb atoms from 0 to 1 has been studied. It has been shown that the Dirac point with an increase in the concentration of Sb atoms is shifted toward the Fermi level and becomes localized at it when x ≈ 0.3. In this case, the “rigid” shift of the valence band, including the Mn 3d level, has been observed without changes in the structure of the valence and conduction bands. The concentration dependence of the shift of the Dirac point is approximated by a square root function, which corresponds to a linear increase in the charge carrier density.)

Шикин А.М., Естюнин Д.А., Зайцев Н.Л., Глазкова Д.А., Климовских И.И., Фильнов С.О., Рыбкин А.Г., Кох К.А., Терещенко О.Е., Звездин К.А., Звездин А.К. Модуляция энергетической запрещенной зоны в точке Дирака в антиферромагнитном топологическом изоляторе MnBi2Te4 как результат изменений поверхностного градиента потенциала // Журнал экспериментальной и теоретической физики. 2022. Т. 161. № 1. С. 126-136. DOI: 10.31857/S0044451022010114 (перевод - Shikin A.M., Estyunin D.A., Glazkova D.A., Klimovskikh I.I., Fil'nov S.O., Rybkin A.G., Kokh K.A., Tereshchenko O.E., Zaitsev N.L., Zvezdin K.A., Zvezdin A.K. Modulation of the Dirac point band gap in the antiferromagnetic topological insulator MnBi2Te4 due to the surface potential gradient change // Journal of Experimental and Theoretical Physics. 2022. Т. 134. № 1. С. 103-111. DOI: 10.1134/S1063776121120141)

Методами фотоэлектронной спектроскопии с угловым разрешением показана возможность существенного различия величин энергетической запрещенной зоны в точке Дирака в диапазоне от 15 до 55 мэВ для различных образцов антиферромагнитного топологического изолятора MnBi2Te4. Методом теории функционала плотности проведен анализ взаимосвязи величины запрещенной зоны в точке Дирака со значением градиента поверхностного потенциала, изменение которого моделировалось приложением внешнего электрического поля перпендикулярно поверхности (0001) MnBi2Te4. Показана возможность как уменьшения, так и увеличения размеров запрещенной зоны в диапазоне от 5 до 89 мэВ при приложении поля относительно исходного значения 81 мэВ. При приложении поля наблюдалось изменение локализации топологических поверхностных состояний и магнитных моментов поверхностных атомов. Проведенный анализ показывает возможность искусственной модуляции величины запрещенной зоны в точке Дирака в широком энергетическом диапазоне, что может быть использовано для модуляции магнитоэлектрических свойств систем на основе MnBi2Te4 в прикладных исследованиях и задачах. (The possibility of significant modulation of the band gap open at the Dirac point (DP) in the range from 15 to 55 meV for different samples of the antiferromagnetic topological insulator MnBi2Te4 is shown using angle-resolved photoemission spectroscopy. The density functional theory is used to analyze the relation between the gap at the DP and the surface potential gradient, the change of which is modeled by the application of an electric field normal to the (0001) MnBi2Te4 surface. The possibility of both decreasing and increasing the DP gap in the range from 5 to 89 meV with respect to the initial value of 81 meV due to the application of a field is shown. When a field is applied, the localization of topological surface states and the magnetic moments of surface atoms change. Our analysis demonstrates the possibility of an artificial band gap modulation at the DP over a wide energy range, which can be used to modulate the magnetoelectric properties of MnBi2Te4-based systems in applied research and problems.)

Estyunin D.A., Kokh K., Tereshchenko O.E., Shikin A.M., Schwier E.F., Kumar S., Shimada K. Features and applications of the energy shift of the topological surface state // Physical Review B. 2022. Т. 105. № 12. С. 125303. DOI: 10.1103/PhysRevB.105.125303

Contemporary studies of magnetic topological insulators (TIs) aimed at investigating Dirac point (DP) gaps by angle-resolved photoemission spectroscopy (ARPES) require ultrahigh energy, momentum, and spatial resolution. Despite satisfying all these conditions, accurate measurements can be spoiled by the well-known, but often neglected, effect of the energy shift of bands, in particular the topological surface state (TSS), due to sample contamination and irradiation. Thus, in this work we focus on the effect of TI irradiation with laser light (hω=6.3 eV) on the measurability of its electronic structure using the ARPES method. We find that the distribution of the shifted TSS is sufficiently localized and remains stable over time under constant conditions. Therefore, it can be used to store information. The TSS retains its spin pattern regardless of irradiation, as demonstrated by dichroic ARPES measurements. However, irradiation leads to a significant broadening of the TSS, accompanied by a drop in its intensity. All these factors complicate the analysis of the states near the DP and the DP gap size. Finally, using a simple model, we demonstrate the variability of the DP gap over time in the resulting ARPES image, caused by both shift and broadening effects. Thus, accurate values of the DP gap can be obtained by measuring over a relatively small period of time, which is determined by a certain time constant of the energy shift.

Khatchenko Y.E., Yakushev M.V., Ponosov Y.S., Kuznetsova T.V., Seibel C., Bentmann H., Reinert F., Orlita M., Golyashov V., Stepina N.P., Tereshchenko O.E., Mudriy A.V., Kokh K.A., Martin R.W. Structural, optical and electronic properties of the wide bandgap topological insulator Bi1.1Sb0.9Te2S // Journal of Alloys and Compounds. 2022. Т. 890. С. 161824. DOI: 10.1016/j.jallcom.2021.161824

Successful applications of a topological insulator (TI) in spintronics require its bandgap to be wider then in a typical TI and the energy position of the Dirac point in the dispersion relations to be away from the valence and conduction bands. In this study we grew Bi1.1Sb0.9Te2S crystals and examined their elemental composition, structural, optical and electronic properties as well as the electronic band structure. The high structural quality of the grown crystals was established by X-ray diffraction and Raman spectroscopy. Angular resolved photoelectron spectroscopy demonstrated a near parabolic character of the valence and conduction bands and a direct bandgap of 0.36 eV. The dispersion relations also revealed a Dirac cone, confirming the topological insulator nature of this material, with the position of the Dirac point being 100 meV above the valence band maximum. Far infrared reflectivity spectra revealed a plasma edge and two phonon dips. Fitting these spectra with theoretical functions based on the Drude-Lorentz model allows determination of the high frequency dielectric constant (41.3), plasma frequency (936 cm−1) and the frequencies of two infrared phonons (177.7 cm−1 and 77.4 cm−1).

Stepina N.P., Golyashov V.A., Nenashev A.V., Tereshchenko O.E., Kirienko V.V., Koptev E.S., Antonova I.V., Kokh K.A., Goldyreva E.S., Rybin M.G., Obraztsova E.D. Weak antilocalization to weak localization transition in Bi2Se3 films on graphene // Physica E: Low-Dimensional Systems and Nanostructures. 2022. Т. 135. С. 114969. DOI: 10.1016/j.physe.2021.114969

Magneto-transport properties were studied on thin films of a 3D topological insulator (TI) Bi2Se3 grown on graphene (Gr) by physical vapor deposition. It was shown that the main contribution to the conductance is from the bulk states, whereas magnetoresistance is determined by both surface and bulk channels. The input of the charge transport over the surface states in the Si/SiO2/Gr/Bi2Se3 structure reveals itself in the weak antilocalization effect. The transition from a weak antilocalization to a weak localization is observed with decreasing the film thickness. The band bending on both interfaces makes it possible to explain the contribution to a weak antilocalization from different surfaces at different TI film thicknesses.

Zhevstovskikh I.V., Sarychev M.N., Averkiev N.S., Semenova O.I., Tereshchenko O.E. Low-temperature luminescence in organic-inorganic lead iodide perovskite single crystals // Journal of Physics D: Applied Physics. 2022. Т. 55. № 9. С. 095105. DOI: 10.1088/1361-6463/ac38e3

We present a temperature and laser-power dependent photoluminescence (PL) study of methylammonium lead iodide (CH3NH3PbI3) single crystals in the orthorhombic phase. At temperatures below 140 K, we revealed the multi-component PL emission. In addition to a free exciton with an energy of 1.65 eV, we found emission bands with peaks approximately equal to 1.6 eV, 1.52 eV, and 1.48 eV. Analysis of the thermal evolution of the intensities, peak positions, and linewidths of all the PL bands allowed one to determine their origin. We attributed the PL peak with energy of 1.6 eV to a bound exciton, while the free exciton-bound exciton splitting energy is 50-60 meV. The PL emission with an energy of 1.52 eV can be explained by the donor-acceptor pair (DAP) recombination, where donor and acceptor defects have a depth of about 12 meV and 120 meV, respectively. MA (CH3NH3) interstitials (MAi+) and lead vacancies (VPb2-) are the most suitable for the DAP transition to occur in CH3NH3PbI3 crystals. The 1.48 eV PL emission is consistent with the recombination of self-trapped excitons, and interstitial iodine is likely to be an active trap source. We found the variation of the self-trapped depth from 15 meV (at T < 80 K) to 53 meV (at T > 80 K) with increasing the temperature. Although the multi-component PL emission in CH3NH3PbI3 single crystals appears at low temperatures, defects and excitonic traps that cause this emission can affect the photophysics of hybrid perovskites at higher temperatures.

2021

Ищенко Д.В., Акимов А.Н., Ахундов И.О., Голяшов В.А., Климов А.Э., Логинов А.Б., Логинов Б.А., Пащин Н.С., Тарасов А.С., Федосенко Е.В., Шерcтякова В.Н. Зависимость топологии эпитаксиальных слоев PbSnTe: In от концентрации In // Журнал технической физики. 2021. Т. 91. № 6. С. 1040-1044. DOI: 10.21883/JTF.2021.06.50876.326-20 (перевод - Ishchenko D.V., Akimov A.N., Akhundov I.O., Golyashov V.A., Klimov A.E., Pashchin N.S., Tarasov A.S., Fedosenko E.V., Sherstyakova V.N., Loginov A.B., Loginov B.A. Topology of PbSnTe: In layers versus indium concentration // Technical Physics. 2022. Т. 66. С. 878-882. DOI: 10.1134/S1063784221060086)

Методом атомно-силовой микроскопии исследована топология поверхности эпитаксиальных пленок твердого раствора теллурида свинца и олова, в том числе с добавлением индия (Pb1-xSnxTe: In), выращенных на монокристаллических подложках BaF2(111) и буферном слое CaF2/BaF2 на Si(111). Показано, что характерные статистические показатели рельефа обусловлены особенностями роста пленки и механизмом встраивания индия, избыточное содержание которого зарегистрировано на поверхности ex situ методом рентгеновской фотоэлектронной спектроскопии. (The surface topology of epitaxial films of lead tin telluride solid solution (including with In additive, Pb1-xSnxTe: In) has been examined using atomic force microscopy. The films have been grown on BaF2(111) single-crystal substrates and on a CaF2/BaF2 buffer layer covering a Si(111) wafer. It has been shown that the relief statistical parameters depend on film growth conditions and the incorporation mechanism of indium, an excess amount of which has been detected on the surface by ex situ XPS.)

Кавеев А.К., Бондаренко Д.Н., Терещенко О.Е. Структурные свойства тонких пленок кристаллического топологического изолятора Pb0.7Sn0.3Te на Si(111) // Физика и техника полупроводников. 2021. Т. 55. № 8. С. 625-628. DOI: 10.21883/FTP.2021.08.51126.02 (перевод - Kaveev A.K., Bondarenko D.N., Tereshchenko O.E. Structural characterization of Pb0.7Sn0.3Te crystalline topological insulator thin films grown on Si(111) // Semiconductors. 2022. Т. 55. С. 682-685. DOI: 10.1134/S106378262108011X)

Проведен подбор и оптимизация технологических параметров роста методом молекулярно-лучевой эпитаксии тонких слоев Pb0.7Sn0.3Te толщиной до 300 нм, выращенных на поверхности Si(111) при температурах 230-400°C, изучена морфология поверхности полученных пленок, определены эпитаксиальные соотношения. Показано, что в зависимости от температуры роста морфология поверхности имеет вид от гладких островов микронного размера, имеющих на поверхности моноатомные ступени, до более узких террас. (Selection and optimization of the technological parameters of growth of Pb0.7Sn0.3Te layers with a thickness up to 300 nm grown on a Si(111) surface at a temperature of 230 to 400°C is carried out. The surface morphology of the resulting films is studied, and the epitaxial relations are determined. It is shown that, depending on the growth temperature, the surface morphology ranges from smooth micrometer-sized islands with monoatomic steps on their surface to narrower terraces.)

Русецкий В.С., Голяшов В.А., Миронов А.В., Дёмин А.Ю., Терещенко О.Е. Фотоэмиссионные свойства мультищелочного фотокатода // Автометрия. 2021. Т. 57. № 5. С. 70-76. DOI: 10.15372/AUT20210508 (перевод - Rusetsky V.S., Golyashov V.A., Tereshchenko O.E., Mironov A.V., Demin A.Y. Photoemission properties of a multialkali photocathode // Optoelectronics, Instrumentation and Data Processing. 2021. Т. 57. № 5. С. 505-510. DOI: 10.3103/S8756699021050149)

Продемонстрирована возможность исследований фотоэмиссионных свойств мультищелочных фотокатодов (МФ) в вакуумных фотодиодах с двумя полупроводниковыми электродами. Исследованы спектральные зависимости фотолюминесценции и квантового выхода МФ, впервые получены спектры распределения фотоэлектронов по энергиям в МФ с высоким разрешением. Измерения проводились при освещении МФ монохроматичным светом в диапазоне длин волн 400-950 нм и температурном интервале 90-300 К. На основе полученных данных сделаны выводы о наличии эффективного отрицательного электронного сродства в МФ. Изучены свойства исследуемого вакуумного фотодиода как солнечного элемента. (The feasibility of studies on the photoemission properties of multialkali photocathodes (MPs) in vacuum photodiodes with two semiconductor electrodes was demonstrated. The photoluminescence and quantum yield spectra were studied, and the high-resolution energy distribution curves of photoelectrons emitted from the MP were taken for the first time. Measurements were performed on multialkali photocathodes illuminated with monochromatic light within a wavelength range of 400–950 nm in a temperature range of 90–300 K. Based on the obtained data, the conclusion, that the MP is a negative electron affinity photocathode, was made. The properties of the solar element based on the studied vacuum photodiode were investigated.)

Талочкин А.Б., Кох К.А., Терещенко О.Е. Спектр оптических фононов монокристалла Ge2Sb2Te5 // Письма в Журнал экспериментальной и теоретической физики. 2021. Т. 113. № 9-10 (5). С. 683-688. DOI: 10.31857/S1234567821100086 (перевод - Talochkin A.B., Tereshchenko O.E., Kokh K.A. Optical phonon spectrum of the Ge2Sb2Te5 single crystal // JETP Letters. 2021. Т. 113. № 10. С. 651-656. DOI: 10.1134/S002136402110012X)

Впервые исследованы спектры комбинационного рассеяния света на оптических фононах монокристалла Ge2Sb2Te5, полученного методом Бриджмена. При другом способе получения этого соединения, связанном с отжигом аморфного состояния и использованном в многочисленных исследованиях ранее, происходит образование различных дефектов, которые кардинально влияют на спектр оптических фононов. Это приводит к неопределенности в идентификации наблюдаемых фононных спектров. Поэтому использование объемного монокристалла Ge2Sb2Te5 позволило исключить влияние решеточных дефектов и выявить новые особенности фононного спектра, связанные со структурой решетки. В спектрах наблюдались широкие особенности, типичные для аморфного состояния материала, а также узкие фононные линии кристаллического состояния. Показано, что первая компонента связана с разупорядоченностью, возникающей из-за перемешивания атомов Ge и Sb в соответствующих слоях решетки. Кроме того, существуют оптические фононы, частоты которых не зависят от этого перемешивания в силу специфики их нормальных координат. Эти моды проявляются в спектрах в виде узких интенсивных линий. (Raman scattering by optical phonons of the Ge2Sb2Te5 single crystal grown by the Bridgman method is studied for the first time. Another method for obtaining this compound based on annealing of the amorphous state and used in numerous previous studies leads to the formation of various defects which significantly affect the optical phonons spectrum. This hampers the identification of observed phonon spectra. The use of the bulk Ge2Sb2Te5 single crystal has made it possible to exclude the effect of lattice defects and to reveal new features of the phonon spectrum associated with the lattice structure. Broad features typical of the amorphous state and narrow phonon lines of the crystal state are observed in the spectra. It has been shown that the former component is due to disorder appearing because of the mixing of Ge and Sb atoms in corresponding layers of the lattice. Moreover, there are optical phonons whose frequencies are independent of this mixing in view of the specificity of their eigenvectors. These modes are manifested in spectra as intense narrow lines.)

Тарасов А.С., Михайлов Н.Н., Дворецкий С.А., Менщиков Р.В., Ужаков И.Н., Кожухов А.С., Федосенко Е.В., Терещенко О.Е. Получение атомарно-чистых и структурно-упорядоченных поверхностей эпитаксиальных пленок CdTe для последующей эпитаксии // Физика и техника полупроводников. 2021. Т. 55. № 9. С. 748-753. DOI: 10.21883/FTP.2021.09.51289.18 (перевод - Tarasov A.S., Mikhailov N.N., Dvoretsky S.A., Menshchikov R.V., Uzhakov I.N., Kozhukhov A.S., Fedosenko E.V., Tereshchenko O.E. Preparation of atomically clean and structurally ordered surfaces of epitaxial CdTe films for subsequent epitaxy // Semiconductors. 2021. Т. 55. № Suppl. 1. С. S62-S66. DOI: 10.1134/S1063782621090220)

Получена атомарно-чистая и структурно-упорядоченная поверхность слоя CdTe подложки (013) GaAs/ZnTe/CdTe после хранения на воздухе с помощью обработки в изопропиловом спирте, насыщенном парами соляной кислоты, и дальнейшего термического отжига в сверхвысоком вакууме. Показано, что химическая обработка поверхности CdTe приводит к удалению собственных оксидов и обогащению поверхности слоем элементного теллура. Во время прогрева в вакууме наблюдается две стадии изменения состояния поверхности (~125°С и ≤ 250°С). При T>250°С происходят десорбция элементного теллура и формирование Te-стабилизированной структуры (1×1) CdTe (013). (An atomically clean and structurally ordered surface of the CdTe layer of a (013)-oriented GaAs/ZnTe/CdTe substrate after storage in air is obtained by treatment in isopropyl alcohol saturated with hydrochloric-acid vapors, with subsequent thermal annealing in ultrahigh vacuum. It is shown that chemical treatment of the CdTe surface results in the removal of native oxides and in enrichment of the surface with an elemental Te layer. During heating in vacuum, two stages of change in the state of the surface (at ~125 and ≤250°C) are observed. At the temperature T > 250°C, elemental tellurium is desorbed, and a Te-stabilized (1 × 1) CdTe(013) structure is formed.)

Antonova I.V., Nebogatikova N.A., Stepina N.P., Volodin V.A., Kirienko V.V., Golyashov V.A., Tereshchenko O.E., Kokh K.A., Rybin M.G., Obrazstova E.D. Growth of Bi2Se3/graphene heterostructures with the room temperature high carrier mobility // Journal of Materials Science. 2021. Т. 56. № 15. С. 9330-9343. DOI: 10.1007/s10853-021-05836-y

Heterostructures ofBi2Se3 topological insulators were epitaxially grown on graphene by means of the physical vapor deposition at 500 °C. Micrometer-sized flakes with thickness 1 QL (quintuple layer ~ 1 nm) and films of millimeter-scale with thicknesses 2–6 QL had been grown on CVD graphene. The minimum thickness of large-scaled continuous Bi2Se3 films was found to be ~ 8 QL for the regime used. The heterostructures with a Bi2Se3 film thickness of > 10 QL had resistivity as low as 200–500 Ω/sq and a high room temperature carrier mobility ~ 1000–3400 cm2/Vs in the Bi2Se3/graphene interface channel. Moreover, the coexistence of a p-type graphene-related conductive channel, simultaneously with the n-type conductive surface channel of Bi2Se3, was observed. The improvement of the bottom Bi2Se3/graphene interface with the increase in the growth time clearly manifested itself in the increase of conductivity and carrier mobility in the grown layer. The grown Bi2Se3/G structures have lower resistivities and more than one order of magnitude higher carrier mobilities in comparison with the van der Waals Bi2Se3/graphene heterostructures created employing exfoliation of thin Bi2Se3 layers. The grown heterostructures demonstrated the properties that are perspective for new functional devices, for a variety of signal processing and logic applications.

Bentmann H., Maaß H., Seibel C., Reinert F., Braun J., Ebert H., Kokh K.A., Tereshchenko O.E., Schreyeck S., Brunner K., Molenkamp L.W., Miyamoto K., Arita M., Shimada K., Okuda T., Kirschner J., Tusche C., Minár J. Profiling spin and orbital texture of a topological insulator in full momentum space // Physical Review B. 2021. Т. 103. № 16. С. L161107. DOI: 10.1103/PhysRevB.103.L161107

We investigate the coupled spin and orbital textures of the topological surface state in Bi2(Te,Se)3(0001) across full momentum space using spin- and angle-resolved photoelectron spectroscopy and relativistic one-step photoemission theory. For an approximately isotropic Fermi surface in Bi2Te2Se, the measured intensity and spin momentum distributions, obtained with linearly polarized light, qualitatively reflect the orbital composition and the orbital-projected in-plane spin polarization, respectively. In Bi2Te3, the in-plane lattice potential induces a hexagonal anisotropy of the Fermi surface, which manifests in an out-of-plane photoelectron spin polarization with a strong dependence on light polarization, excitation energy, and crystallographic direction.

Faidiuk Y., Skivka L., Zelena P., Tereshchenko O., Buluy O., Pergamenshchik V.M., Nazarenko V. Anchoring-induced nonmonotonic velocity versus temperature dependence of motile bacteria in a lyotropic nematic liquid crystal // Physical Review E. 2021. Т. 104. № 5. С. 054603. DOI: 10.1103/PhysRevE.104.054603

The elastic and viscous properties of lyotropic chromonic liquid crystals have a very sharp, often exponential temperature dependence. Self-propelled bacteria swimming in this viscoelastic medium induce director deformations which can strongly influence their velocity, and we study the temperature behavior of their motility in the whole range of the nematic phase. We observe experimentally that, with increasing temperature, while the viscosity drops exponentially and the frequency of the flagellum rotation grows linearly, the swimmers' speed first conventionally increases but then, above some crossover temperature, slows down and at the same time bacteria-induced director distortions become visible. It is shown that the physics behind this temperature-driven effect is in a sharp rise in the ability of the bacterium's flagellum to induce director deformations. As temperature increases, the splay and bend elastic constants sharply decrease and the anchoring extrapolation length of the flagellum surface gets shorter and shorter. At the crossover temperature the resulting effective anchoring effect dominates the fast dropping viscosity and the distortion strengthens. As a result, a fraction of the torque the flagellum applies for the propulsion is spent for the elastic degrees of freedom, which results in a bacterium slowdown. To find the director distortions, the flagellum is presented as a collection of anchoring-induced elastic monopoles, and the bacterium velocity is found from the balance of the energy spent for the propulsion and the viscous drag and nematodynamic dissipation.

Kaveev A.K., Suturin S.M., Golyashov V.A., Tereshchenko O.E., Kokh K.A., Eremeev S.V., Estyunin D.A., Shikin A.M., Okotrub A.V., Lavrov A.N., Schwier E.F. Band gap opening in the BiSbTeSe2 topological surface state induced by ferromagnetic surface reordering // Physical Review Materials. 2021. Т. 5. № 12. С. 124204. DOI: 10.1103/PhysRevMaterials.5.124204

Introducing magnetic exchange interaction into topological insulators is known to break the time-reversal symmetry and to open a gap at the Dirac point in the otherwise gapless topological surface states. This allows various novel topological quantum phenomena to be attained, including the quantum anomalous Hall effect and can lead to the emergence of the axion insulator phase. Among the different approaches, magnetic doping is an effective, but still experimentally challenging pathway to provide the magnetic exchange interaction. Here we demonstrate that epitaxial deposition of Co and Mn magnetic atoms onto the (0001) surface of the BiSbTeSe2 topological insulator with a coverage between 0.6 and 3 atoms per surface cell performed in a finely tuned temperature range of 300°-330°C leads to the substitution of pnictogen atoms in the surface layer with magnetic atoms and to the formation of a two-dimensional magnetic phase with out-of-plane magnetization as proved by SQUID magnetometry. This magnetic layer is responsible for the appearance of a gap in the Dirac surface state as revealed by laser-based microfocused angle-resolved photoelectron spectroscopy. Our measurements have shown that the gap exists within the temperature range of 15-100 K, where the out-of-plane magnetization persists. The presented experimental results are supported by relativistic ab initio calculations.

Ketterl A.S., Andres B., Polverigiani M., Gahl C., Weinelt M., Voroshnin V., Chulkov E.V., Shikin A., Kokh K.A., Tereshchenko O.E. Effect of Rashba splitting on ultrafast carrier dynamics in BiTeI // Physical Review B. 2021. Т. 103. № 8. С. 085406. DOI: 10.1103/PhysRevB.103.085406

Narrow-gap semiconductors with strong spin-orbit coupling such as bismuth tellurohalides have become popular candidates for spintronic applications. But driving spin-polarized photocurrents in these materials with circularly polarized light requires picosecond lifetimes of the photoexcited carriers and low spin-flip scattering rates. In search of these essential ingredients, we conducted an extensive study of the carrier dynamics on the Te-terminated surface of BiTeI, which exhibits a giant Rashba splitting of both surface and bulk states. We observe a complex interplay of surface and bulk dynamics after photoexcitation. Carriers are rapidly rearranged in momentum space by quasielastic phonon and defect scattering, while a phonon bottleneck leads to a slow equilibration between bulk electrons and lattice. The particular band dispersion opens an inelastic decay channel for hot carriers in the form of plasmon excitations, which are immanent to Rashba-split systems. These ultrafast scattering processes effectively redistribute excited carriers in momentum and energy space and thereby inhibit spin-polarized photocurrents.

Kocsis M., Makk P., Tóvári E., Csonka S., Zheliuk O., Ye J., Kun P., Tereshchenko O.E., Kokh K.A., Taniguchi T., Watanabe K. In situ tuning of symmetry-breaking-induced nonreciprocity in the giant-Rashba semiconductor BiTeBr // Physical Review Research. 2021. Т. 3. № 3. С. 033253. DOI: 10.1103/PhysRevResearch.3.033253

Nonreciprocal transport, where the left-to-right-flowing current differs from the right-to-left-flowing one, is an unexpected phenomenon in bulk crystals. BiTeBr is a noncentrosymmetric material, with a giant Rashba spin-orbit coupling which presents this unusual effect when placed in an in-plane magnetic field. It has been shown that this effect depends strongly on the carrier density; however, in situ tuning has not yet been demonstrated. We developed a method where thin BiTeBr flakes are gate tuned via ionic-liquid gating through a thin protective hexagonal boron nitride layer. Tuning the carrier density allows a more than 400% variation of the nonreciprocal response in our sample. Our study demonstrates how a few-atomic-layer-thick van der Waals protection layer allows ionic gating of chemically sensitive, exotic nanocrystals.

Riha C., Düzel B., Graser K., Chiatti O., Fischer S.F., Golias E., Sánchez-Barriga J., Rader O., Tereshchenko O.E. Electrical transport properties of vanadium-doped Bi2Te2.4Se0.6 // Physica Status Solidi (B): Basic Solid State Physics. 2021. Т. 258. № 1. С. 2000088. DOI: 10.1002/pssb.202000088

Vanadium-doped Bi2–xTe2.4Se0.6 single crystals, with x = 0.015 and 0.03, are grown by the Bridgman method. Bandstructure characterization by angle-resolved photoemission spectroscopy (ARPES) measurements shows gapless topological surface states for both vanadium concentrations. The Van-der-Pauw resistivity, the Hall charge carrier density, and the mobility in the temperature range from 0.3 to 300 K are strongly dependent on vanadium concentration, with carrier densities as low as 1.5 × 1016 cm−3 and mobilities as high as 570 cm2 V−1 s−1. As expected for transport in gapless topological surface states, the resistivity, carrier density, and mobility are constant below 10 K. The magnetoresistance shows weak antilocalization for both vanadium concentrations in the same temperature range. The weak antilocalization is analyzed with the Hikami–Larkin–Nagaoka model, which yields phase-coherence lengths of up to 250 nm for x = 0.015.

Schmid C.P., Weigl L., Schlauderer S., Meierhofer M., Hofmann N., Afanasiev D., Huber R., Grössing P., Junk V., Gorini C., Crewse J., Evers F., Wilhelm J., Richter K., Ito S., Güdde J., Höfer U., Kokh K.A., Tereshchenko O.E. Tunable non-integer high-harmonic generation in a topological insulator Nature. 2021. Т. 593. № 7859. С. 385-390. DOI: 10.1038/s41586-021-03466-7

When intense lightwaves accelerate electrons through a solid, the emerging high-order harmonic (HH) radiation offers key insights into the material. Sub-optical-cycle dynamics—such as dynamical Bloch oscillations, quasiparticle collisions, valley pseudospin switching and heating of Dirac gases—leave fingerprints in the HH spectra of conventional solids. Topologically non-trivial matter with invariants that are robust against imperfections has been predicted to support unconventional HH generation. Here we experimentally demonstrate HH generation in a three-dimensional topological insulator—bismuth telluride. The frequency of the terahertz driving field sharply discriminates between HH generation from the bulk and from the topological surface, where the unique combination of long scattering times owing to spin–momentum locking17 and the quasi-relativistic dispersion enables unusually efficient HH generation. Intriguingly, all observed orders can be continuously shifted to arbitrary non-integer multiples of the driving frequency by varying the carrier-envelope phase of the driving field—in line with quantum theory. The anomalous Berry curvature warranted by the non-trivial topology enforces meandering ballistic trajectories of the Dirac fermions, causing a hallmark polarization pattern of the HH emission. Our study provides a platform to explore topology and relativistic quantum physics in strong-field control, and could lead to non-dissipative topological electronics at infrared frequencies.

Shikin A.M., Estyunin D.A., Glazkova D., Klimovskikh I.I., Filnov S.O., Rybkin A.G., Kokh K., Tereshchenko O.E., Otrokov M.M., Chulkov E.V., Zvezdin K.A., Zvezdin A.K., Zaitsev N.L., Schwier E.F., Kumar S., Kimura A., Mamedov N., Aliev Z., Babanly M.B. Sample-dependent Dirac-point gap in and its response to applied surface charge: a combined photoemission and ab initio study // Physical Review B. 2021. Т. 104. № 11. С. 115168. DOI: 10.1103/PhysRevB.104.115168

Recently discovered intrinsic antiferromagnetic topological insulator MnBi2Te4 presents an exciting platform for realization of the quantum anomalous Hall effect and a number of related phenomena at elevated temperatures. An important characteristic making this material attractive for applications is its predicted large magnetic gap at the Dirac point (DP). However, while the early experimental measurements reported on large DP gaps, a number of recent studies claimed to observe a gapless dispersion of the MnBi2Te4 Dirac cone. Here, using micro(μ)-laser angle-resolved photoemission spectroscopy, we study the electronic structure of 15 different MnBi2Te4 samples, grown by two different chemists groups. Based on the careful energy distribution curves analysis, the DP gaps between 15 and 65 meV are observed, as measured below the Néel temperature at about 10–16 K. At that, roughly half of the studied samples show the DP gap of about 30 meV, while for a quarter of the samples the gaps are in the 50 to 60 meV range. Summarizing the results of both our and other groups, in the currently available MnBi2Te4 samples the DP gap can acquire an arbitrary value between a few and several tens of meV. Furthermore, based on the density functional theory, we discuss a possible factor that might contribute to the reduction of the DP gap size, which is the excess surface charge that can appear due to various defects in surface region. We demonstrate that the DP gap is influenced by the applied surface charge and even can be closed, which can be taken advantage of to tune the MnBi2Te4 DP gap size.

Shikin A.M., Rybkina A.A., Estyunin D.A., Klimovskikh I.I., Rybkin A.G., Filnov S.O., Koroleva A.V., Shevchenko E.V., Likholetova M.V., Voroshnin V.Y., Petukhov A.E., Kokh K.A., Tereshchenko O.E., Petaccia L., Di Santo G., Kumar S., Kimura A., Skirdkov P.N., Zvezdin K.A., Zvezdin A.K. Non-monotonic variation of the Kramers point band gap with increasing magnetic doping in BiTeI // Scientific Reports. 2021. Т. 11. № 1. С. 23332. DOI: 10.1038/s41598-021-02493-8

Polar Rashba-type semiconductor BiTeI doped with magnetic elements constitutes one of the most promising platforms for the future development of spintronics and quantum computing thanks to the combination of strong spin-orbit coupling and internal ferromagnetic ordering. The latter originates from magnetic impurities and is able to open an energy gap at the Kramers point (KP gap) of the Rashba bands. In the current work using angle-resolved photoemission spectroscopy (ARPES) we show that the KP gap depends non-monotonically on the doping level in case of V-doped BiTeI. We observe that the gap increases with V concentration until it reaches 3% and then starts to mitigate. Moreover, we find that the saturation magnetisation of samples under applied magnetic field studied by superconducting quantum interference device (SQUID) magnetometer has a similar behaviour with the doping level. Theoretical analysis shows that the non-monotonic behavior can be explained by the increase of antiferromagnetic coupled atoms of magnetic impurity above a certain doping level. This leads to the reduction of the total magnetic moment in the domains and thus to the mitigation of the KP gap as observed in the experiment. These findings provide further insight in the creation of internal magnetic ordering and consequent KP gap opening in magnetically-doped Rashba-type semiconductors.

Tarasov A.S., Ishchenko D.V., Akhundov I.O., Golyashov V.A., Klimov A.E., Suprun S.P., Fedosenko E.V., Sherstyakova V.N., Tereshchenko O.E., Rybkin A.G., Vilkov O.Y. Surface chemical treatment effect on (1 1 1) PbSnTe < In > topological crystalline insulator films // Applied Surface Science. 2021. Т. 569. С. 150930. DOI: 10.1016/j.apsusc.2021.150930

In present work, the effect of Pb1-xSnxTe < In > (1 1 1) surface chemical treatment on electrophysical and optical properties was studied. It was shown that treatment of Pb1-xSnxTe < In > (1 1 1) surface in HCl-isopropanol (HCl-iPA) solution led to removal of native oxides and surface enrichment by elemental tellurium of several nm thickness. Subsequent anneals in vacuum led to desorption of elemental tellurium and revealing (1×1) surface structure. We present angle resolved photoemission spectroscopy (ARPES) measurements of the surface states on chemically prepared (1 1 1) oriented MBE-grown films of Pb1-xSnxTe, a three-dimensional topological crystalline insulator (TCI). The surface states with Dirac-like dispersion at Γ in the surface Brillouin zone were detected. The dark current and photocurrent were found in strong dependence on the surface chemical procedure and composition. The relative simplicity of the preparation technique is encouraging, and suggests a clear path for future investigations of TCI states on alternative surface orientations in (Pb,Sn)Te solid solutions and applied aspects of TCI research.

Tereshchenko O.E., Golyashov V.A., Rusetsky V.S., Mironov A.V., Demin A.Y., Aksenov V.V. A new imaging concept in spin polarimetry based on the spin-filter effect // Journal of Synchrotron Radiation. 2021. Т. 28. С. 864-875. DOI: 10.1107/S1600577521002307

The concept of an imaging-type 3D spin detector, based on the combination of spin-exchange interactions in the ferromagnetic (FM) film and spin selectivity of the electron-photon conversion effect in a semiconductor heterostructure, is proposed and demonstrated on a model system. This novel multichannel concept is based on the idea of direct transfer of a 2D spin-polarized electron distribution to image cathodoluminescence (CL). The detector is a hybrid structure consisting of a thin magnetic layer deposited on a semiconductor structure allowing measurement of the spatial and polarization-dependent CL intensity from injected spin-polarized free electrons. The idea is to use spin-dependent electron transmission through in-plane magnetized FM film for in-plane spin detection by measuring the CL intensity from recombined electrons transmitted in the semiconductor. For the incoming electrons with out-of-plane spin polarization, the intensity of circularly polarized CL light can be detected from recombined polarized electrons with holes in the semiconductor. In order to demonstrate the ability of the solid-state spin detector in the image-type mode operation, a spin detector prototype was developed, which consists of a compact proximity focused vacuum tube with a spin-polarized electron source [p-GaAs(Cs,O)], a negative electron affinity (NEA) photocathode and the target [semiconductor heterostructure with quantum wells also with NEA]. The injection of polarized low-energy electrons into the target by varying the kinetic energy in the range 0.5-3.0 eV and up to 1.3 keV was studied in image-type mode. The figure of merit as a function of electron kinetic energy and the target temperature is determined. The spin asymmetry of the CL intensity in a ferromagnetic/semiconductor (FM-SC) junction provides a compact optical method for measuring spin polarization of free-electron beams in image-type mode. The FM-SC detector has the potential for realizing multichannel 3D vectorial reconstruction of spin polarization in momentum microscope and angle-resolved photoelectron spectroscopy systems.

2020

Акимов А.Н., Ахундов И.О., Ищенко Д.В., Климов А.Э., Неизвестный И.Г., Пащин Н.С., Супрун С.П., Тарасов А.С., Терещенко О.Е., Федосенко Е.В., Шерстякова В.Н. Знакопеременная фотопроводимость в пленках PbSnTe : In в режиме тока, ограниченного пространственным зарядом // Физика и техника полупроводников. 2020. Т. 54. № 8. С. 796-800. DOI: 10.21883/FTP.2020.08.49628.04 (перевод - Akimov A.N., Akhundov I.O., Ishchenko D.V., Klimov A.E., Neizvestny I.G., Paschin N.S., Suprun S.P., Tarasov A.S., Tereshchenko O.E., Fedosenko E.V., Sherstyakova V.N. Sign-alternating photoconductivity in PbSnTe: In films in the space-charge-limited current regime // Semiconductors. 2020. Т. 54. № 8. С. 951-955. DOI: 10.1134/S1063782620080035)

В режиме тока, ограниченного пространственным зарядом, в пленках PbSnTe: In обнаружена зависимость знака фотопроводимости от напряжения смещения, интенсивности и времени освещения. Рассматривается роль ловушек со сложным энергетическим спектром, включая поверхностные, в наблюдаемых эффектах. Ключевые слова: фотопроводимость, примесные состояния, поверхностные состояния, PbSnTe. (The dependence of the photoconductivity sign on the bias voltage, intensity, and duration of illumination is studied for PbSnTe: In films in the space-charge-limited current regime. The role of traps (including surface ones) with a complex energy spectrum in the effects under observation is discussed.)

Иконников А.В., Дудин В.C., Артамкин А.И., Акимов А.Н., Климов А.Э., Терещенко О.Е., Рябова Л.И., Хохлов Д.Р. Оптические и транспортные свойства эпитаксиальных пленок Pb0.74Sn0.26Te(In) с модифицируемой поверхностью // Физика и техника полупроводников. 2020. Т. 54. № 9 (9833). С. 896-901. DOI: 10.21883/FTP.2020.09.49828.20 (перевод - Ikonnikov A.V., Dudin V.S., Artamkin A.I., Ryabova L.I., Khokhlov D.R., Akimov A.N., Klimov A.E., Tereshchenko O.E. Optical and transport properties of epitaxial Pb0.74Sn0.26Te(In) films with a modifiable surface // Semiconductors. 2020. Т. 54. № 9. С. 1086-1091. DOI: 10.1134/S1063782620090134)

Представлены результаты исследований оптических и транспортных свойств эпитаксиальных пленок Pb0.74Sn0.26Te(In) с различной обработкой поверхности. Сравнительный анализ полученных данных позволил установить, что характерные особенности спектров фотопроводимости определяются процессами в объеме пленки, а поверхностные состояния на спектры практически не влияют. При этом кинетика фотоотклика и скорость релаксационных процессов в существенной степени зависят от состояния поверхности. Характерные времена релаксации неравновесных носителей заряда (порядка нескольких мс) позволяют использовать методы стандартной Фурье-спектроскопии для характеризации оптических переходов в объеме. (The results of studies of the optical and transport properties of epitaxial Pb0.74Sn0.26Te(In) films with a differently treated surface are presented. A comparative analysis of the results makes it possible to establish that the characteristic features of the photoconductivity spectra are defined by processes in the bulk while the surface states have practically no effect on the spectra. At the same time, the photoresponse kinetics and the rate of relaxation processes are heavily dependent on the state of the surface. The characteristic relaxation times of nonequilibrium charge carriers (about several milliseconds) are such that it is possible to use the methods of standard Fourier-transform spectroscopy to characterize optical transitions in the bulk.)

Кавеев А.К., Банщиков А.Г., Терпицкий А.Н., Голяшов В.А., Терещенко О.Е., Кох К.А., Естюнин Д.А., Шикин А.М. Раскрытие энергетической щели в области точки Дирака при осаждении кобальта на поверхность (0001) топологического изолятора BiSbTeSe2 // Физика и техника полупроводников. 2020. Т. 54. № 9 (9833). С. 859-864. DOI: 10.21883/FTP.2020.09.49821.13 (перевод - Kaveev A.K., Banshchikov A.G., Terpitskiy A.N., Golyashov V.A., Tereshchenko O.E., Kokh K.A., Estyunin D.A., Shikin A.M. Energy-gap opening near the Dirac point after the deposition of cobalt on the (0001) surface of the topological insulator BiSbTeSe2 // Semiconductors. 2020. Т. 54. № 9. С. 1051-1055. DOI: 10.1134/S1063782620090146)

Впервые показано, что субнанометровые покрытия Со, нанесенные методом молекулярно-лучевой эпитаксии на поверхность (0001) топологического изолятора BiSbTeSe2 при температуре 330°C, открывают энергетическую щель в спектре топологических поверхностных состояний в области точки Дирака, со смещением положения точки Дирака, вызванным предварительным осаждением адсорбата при комнатной температуре. Ширина щели составляет 21±6 мэВ. Температурно-зависимые измерения в диапазоне 15-150 K не показали изменения ширины энергетической щели. (It is shown for the first time that Co subnanometer coatings deposited by molecular-beam epitaxy on the (0001) surface of the topological insulator BiSbTeSe2 at a temperature of 330°C open an energy gap in the spectrum of topological surface states in the region of the Dirac point with a shift of the Dirac-point position caused by the preliminary deposition of an adsorbate at room temperature. The gap width is 21 ± 6 meV. Temperature-dependent measurements in the range of 15–150 K show no changes in the energy-gap width.)

Климов А.Э., Акимов А.Н., Ахундов И.О., Голяшов В.А., Горшков Д.В., Ищенко Д.В., Матюшенко Е.В., Неизвестный И.Г., Сидоров Г.Ю., Супрун С.П., Тарасов А.С., Терещенко О.Е., Эпов В.С. Особенности МДП-структур на основе изолирующих пленок PbSnTe : In с составом вблизи инверсии зон, обусловленные их сегнетоэлектрическими свойствами // Физика и техника полупроводников. 2020. Т. 54. № 10 (10987). С. 1122-1128. DOI: 10.21883/FTP.2020.10.49955.29 (перевод - Klimov A.E., Akimov A.N., Akhundov I.O., Golyashov V.A., Gorshkov D.V., Ishchenko D.V., Matyushenko E.V., Neizvestny I.G., Sidorov G.Y., Suprun S.P., Tarasov A.S., Tereshchenko O.E., Epov V.S. Features of mis structures based on insulating PbSnTe: In films with the composition in the vicinity of the band inversion related to their ferroelectric properties // Semiconductors. 2020. Т. 54. № 10. С. 1325-1331. DOI: 10.1134/S1063782620100164)

Исследованы характеристики МДП-структур на основе изолирующих пленок PbSnTe : In с составами вблизи инверсии зон, полученных методом молекулярно-лучевой эпитаксии. Показано, что ряд их особенностей могут быть вызваны сегнетоэлектрическим фазовым переходом с температурой Кюри в области примерно T ~ 15-20 K. (The characteristics of metal-insulator-semiconductor (MIS) structures based on insulating PbSnTe: In films with compositions in the vicinity of band inversion grown by molecular-beam epitaxy (MBE) are studied. It is shown that a number of features of the films can be due to a ferroelectric phase transition with a Curie temperature in the range of about T ≈ 15–20 K.)

Неизвестный И.Г., Ищенко Д.В., Ахундов И.О., Супрун С.П., Терещенко О.Е. О причине деградации буферных слоев CaF2/BaF2 на Si (111) // Доклады Российской академии наук. Физика, технические науки. 2020. Т. 490. № 1. С. 39-42. DOI: 10.31857/S2686740020010174 (перевод - Neizvestny I.G., Ishchenko D.V., Akhundov I.O., Suprun S.P., Tereshchenko O.E. Origin of degradation of the Caf2/Baf2 buffer layers on Si(111) // Doklady Physics. 2020. Т. 65. № 1. С. 15-17. DOI: 10.1134/S1028335820010103)

Исследованы зависимости вольт-фарадных характеристик и химической стойкости буферных слоев CaF2/BaF2, полученных методом молекулярно-лучевой эпитаксии на Si, от температуры роста. Изучение границы раздела системы CaF2/Si методами вторичной ионной масс-спектрометрии и рентгеновской фотоэлектронной спектроскопии позволяет предположить, что наблюдаемые изменения могут быть обусловлены обогащением поверхностного слоя Si кальцием. (The growth temperature dependences of the capacitance–voltage characteristics and chemical stability of the CaF2/BaF2 buffer layers formed on Si by molecular beam epitaxy have been investigated. Secondary ion mass spectrometry and X-ray photoelectron spectroscopy studies of the CaF2/Si interface suggest that the observed variations can be caused by the enrichment of the Si surface layer with calcium.)

Тарасов А.С., Голяшов В.А., Ищенко Д.В., Ахундов И.О., Климов А.Э., Эпов В.С., Кавеев А.К., Супрун С.П., Шерстякова В.Н., Терещенко О.Е. Эффект поля и спин-вентильный эффект в кристаллическом топологическом изоляторе PbSnTe // Автометрия. 2020. Т. 56. № 5. С. 121-126. DOI: 10.15372/AUT20200514 (перевод - Tarasov A.S., Golyashov V.A., Ishchenko D.V., Akhundov I.O., Klimov A.E., Epov V.S., Suprun S.P., Sherstyakova V.N., Tereshchenko O.E., Kaveev A.K. Field effect and spin-valve effect in the PbSnTe topological crystalline insulator // Optoelectronics, Instrumentation and Data Processing. 2020. Т. 56. № 5. С. 553-557. DOI: 10.3103/S8756699020050131)

Исследованы характеристики структур металл-диэлектрик-проводник на основе изолирующих плёнок PbSnTe: In с составами вблизи инверсии зон, полученных методом молекулярно-лучевой эпитаксии. Показано, что ряд их особенностей может быть вызван сегнетоэлектрическим фазовым переходом с температурой Кюри в диапазоне 15-20 К. Получены результаты по инжекции и детектированию спин-поляризованных электронов в PbSnTe: In с использованием ферромагнитных контактов Co и Co40Fe40B20. Обнаружен спин-вентильный эффект при измерении магнетосопротивления в локальной геометрии на удалении ферромагнитных контактов более 30 мкм. Методом фотоэмиссии с угловым и спиновым разрешением показано наличие поверхностного спин-поляризованного состояния с линейным законом дисперсии. (The characteristics of MIS structures based on insulating PbSnTe: In films grown by molecular beam epitaxy (MBE) with compositions near the band inversion are studied. It is shown that a number of their features can be induced by a ferroelectric phase transition with the Curie temperature in the range of 15-20 K. The injection and detection of spin-polarized electrons in PbSnTe: In are studied by using ferromagnetic contacts Co and Co40Fe40B20. A spin-valve effect is discovered by measuring the magnetoresistance in local geometry at a distance of more than 30 mum from ferromagnetic contacts. The presence of a surface spin-polarized state with a linear dispersion law is demonstrated by means of the photoemission with angular and spin resolution.)

Antonova I.V., Nebogatikova N.A., Soots R.A., Golyashov V.A., Tereshchenko O.E., Kokh K.A., Kustov D.A. Electrochemically exfoliated thin Bi2Se3 films and van der Waals heterostructures Bi2Se3/graphene // Nanotechnology. 2020. Т. 31. № 12. С. 125602. DOI: 10.1088/1361-6528/ab5cd5

Thin Bi2Se3 flakes with few nanometer thicknesses and sized up to 350 μm were created by using electrochemical splitting from high-quality Bi2Se3 bulk monocrystals. The dependence of film resistance on the Bi2Se3 flake thickness demonstrates that, at room temperature, the bulk conductivity becomes negligible in comparison with the surface conductivity for films with thicknesses lower than 80 nm. Unexpectedly, all these films demonstrated p-type conductivity. The doping effect with sulfur or sulfur-related radicals during electrochemical exfoliation is suggested for the p-type conductivity of the exfoliated Bi2Se3 films. The formation of 2-8 nm films was predominantly found. Van der Waals (vdW) heterostructures of Bi2Se3/Graphene/SiO2/Si were created and their properties were compared with that of Bi2Se3 on the SiO2/Si substrate. The increase of the conductivity and carrier mobility in Bi2Se3 flakes of 3-5 times was found for vdW heterostructures with graphene. Thin Bi2Se3 films are potentially interesting for applications for spintronics, nano- and optoelectronics.

Golyashov V.A., Rusetsky V.S., Shamirzaev T.S., Dmitriev D.V., Tereshchenko O.E., Kislykh N.V., Mironov A.V., Aksenov V.V. Spectral detection of spin-polarized ultra low-energy electrons in semiconductor heterostructures // Ultramicroscopy. 2020. Т. 218. С. 113076. DOI: 10.1016/j.ultramic.2020.113076

The circularly polarized cathodoluminescence (CL) technique has been used to study the free spin-polarized electron injection in semiconductor heterostructures with quantum wells (QWs). A polarized electron beam was created by the emission of optically oriented electrons from the p-GaAs(Cs,O) negative electron affinity (NEA) photocathode. The prepared beam was injected in a semiconductor QW target, which was activated by cesium and oxygen to reduce the work function. To study the spin-dependent injection, we developed a spin-detector prototype, which consists of a compact proximity focused vacuum tube with the source and target placed parallel to each other on the opposite ends of the vacuum tube (photodiode). The injection of polarized low-energy electrons into the target by varying the kinetic energy in the range of 0.5-5.0 eV and temperature in the range of 90-300 K was studied. The CL was polarized to 2% by the injection of 20 % spin-polarized electron beam with the energy of 0.5 eV at room temperature. The asymmetry (Sherman function) of spin detection was estimated. It was shown that the dependence of the CL polarization degree on the injected electron energy is satisfactory described by the model that considers the electron spin relaxation in the heterostructure matrix and QWs. The results demonstrate that semiconductor detectors are promising for the spin-polarimetry applications based on the optical detection of free-electron spin polarization.

Kaveev A.K., Suturin S.M., Golyashov V.A., Klimov A.E., Tarasov A.S., Tereshchenko O.E., Schwier E.F. Structure and magneto-electric properties of Co-based ferromagnetic films grown on the Pb0.71Sn0.29Te crystalline topological insulator // Materials Chemistry and Physics. 2020. Т. 240. С. 122134. DOI: 10.1016/j.matchemphys.2019.122134

Co, Ni, Co55Fe45 and Co40Fe40B20 layers were grown on Pb0.71Sn0.29Te (111) crystalline topological insulator films by conventional and laser molecular beam epitaxy (LMBE) methods. It was demonstrated that the Co40Fe40B20 ferromagnetic films were grown epitaxially on the crystalline topological insulator surface, with clear epitaxial relations. Obtained Co40Fe40B20 layers have a bcc crystal structure with a crystalline (111) plane parallel to the (111) plane of Pb0.71Sn0.29Te. The use of reciprocal space three-dimensional mapping of reflection high electron diffraction (RHEED) patterns made it possible to determine the epitaxial relations of the film and substrate. Using laser based angle-resolved photoemission spectroscopy (LARPES) the clean Pb0.71Sn0.29Te surface with Dirac-like dispersion of the topological surface states was demonstrated. The stable surface topological state of Pb0.71Sn0.29Te was observed at least at the monolayer thick Co coverage. It was shown that Co (or Ni) and Co55Fe45 may be used as a pair of contacts (injector and detector) with different coercivities for spin transport measurements in the “metal – topological insulator” systems. The measurements of magnetic and transport properties show distinct hysteresis – type dependence of the magnetoresistance in the range of quadratic I(U) dependence.

Klimovskikh I.I., Estyunin D., Eremeev S.V., Filnov S.O., Koroleva A., Shevchenko E., Rybkin A.G., Rusinov I.P., Tereshchenko O.E., Kokh K.A., Shikin A.M., Chulkov E.V., Otrokov M.M., Echenique P.M., Voroshnin V., Blanco-Rey M., Hoffmann M., Ernst A., Aliev Z.S., Amiraslanov I.R., Abdullayev N.A., Mamedov N.T., Babanly M.B., Zverev V.N., Kimura A., Petaccia L., Di Santo G. Tunable 3d/2d magnetism in the (MnBi2Te4)(Bi2Te3)m topological insulators family // npj Quantum Materials. 2020. Т. 5. № 1. С. 54. DOI: 10.1038/s41535-020-00255-9

Feasibility of many emergent phenomena that intrinsic magnetic topological insulators (TIs) may host depends crucially on our ability to engineer and efficiently tune their electronic and magnetic structures. Here we report on a large family of intrinsic magnetic TIs in the homologous series of the van der Waals compounds (MnBi2Te4)(Bi2Te3)m with m = 0, ⋯, 6. Magnetic, electronic and, consequently, topological properties of these materials depend strongly on the m value and are thus highly tunable. The antiferromagnetic (AFM) coupling between the neighboring Mn layers strongly weakens on moving from MnBi2Te4 (m = 0) to MnBi4Te7 (m = 1) and MnBi6Te10 (m = 2). Further increase in m leads to change of the overall magnetic behavior to ferromagnetic (FM) one for (m = 3), while the interlayer coupling almost disappears. In this way, the AFM and FM TI states are, respectively, realized in the m = 0, 1, 2 and m = 3 cases. For large m numbers a hitherto-unknown topologically nontrivial phase can be created, in which below the corresponding critical temperature the magnetizations of the non-interacting 2D ferromagnets, formed by the MnBi2Te4 building blocks, are disordered along the third direction. The variety of intrinsic magnetic TI phases in (MnBi2Te4)(Bi2Te3)m allows efficient engineering of functional van der Waals heterostructures for topological quantum computation, as well as antiferromagnetic and 2D spintronics.

Kokh K.A., Goldyreva E.S., Nebogatikova N.A., Antonova I.V., Tereshchenko O.E., Kustov D.A., Golyashov V.A., Stepina N.P., Kirienko V.V. Vapor growth of Bi2Se3 and Bi2O2Se crystals on mica // Materials Research Bulletin. 2020. Т. 129. С. 110906. DOI: 10.1016/j.materresbull.2020.110906

Thin Bi2Se3 films were deposited on mica substrates by physical vapor deposition without the use of the carrier gas. It was found that the films with high structural quality and high conductivity are grown at a source temperature of approximately 500 °C. The resistance of 20–300 nm thick films is in the range of 102-104 Ω/sq as compared with ~10 Ω/sq for thicker films.Bi2O2Se crystals with a similar resistivity are revealed to grow at higher temperatures (600–700 °C). It was suggested that the decrease of the thin film resistance is due to the contribution of the surface channels. Low resistivity of the Bi2Se3 films expands the scope of their possible applications as infra-red transparent electrodes.

Kovács-Krausz Z., Makk P., Szentpéteri B., Kocsis M., Fülöp B., Csonka S., Hoque A.M., Dash S.P., Yakushev M.V., Kuznetsova T.V., Tereshchenko O.E., Kokh K.A., Lukács I.E., Taniguchi T., Watanabe K. Electrically controlled spin injection from giant Rashba spin-orbit conductor BiTeBr // Nano Letters. 2020. Т. 20. № 7. С. 4782-4791. DOI: 10.1021/acs.nanolett.0c00458

Ferromagnetic materials are the widely used source of spin-polarized electrons in spintronic devices, which are controlled by external magnetic fields or spin-transfer torque methods. However, with increasing demand for smaller and faster spintronic components utilization of spin-orbit phenomena provides promising alternatives. New materials with unique spin textures are highly desirable since all-electric creation and control of spin polarization is expected where the strength, as well as an arbitrary orientation of the polarization, can be defined without the use of a magnetic field. In this work, we use a novel spin-orbit crystal BiTeBr for this purpose. Because of its giant Rashba spin splitting, bulk spin polarization is created at room temperature by an electric current. Integrating BiTeBr crystal into graphene-based spin valve devices, we demonstrate for the first time that it acts as a current-controlled spin injector, opening new avenues for future spintronic applications in integrated circuits.

Nurmamat M., Okamoto K., Zhu S., Miyashita T., Wang X., Sumida K., Menshchikova T.V., Rusinov I.P., Korostelev V.O., Miyamoto K., Okuda T., Schwier E.F., Shimada K., Ishida Y., Kimura A., Shin S., Ye M., Aliev Z.S., Amiraslanov I.R., Babanly M.B., Chulkov E.V., Kokh K.A., Tereshchenko O.E. Topologically nontrivial phase-change compound GeSb2Te4 // ACS Nano. 2020. Т. 14. № 7. С. 9059-9065. DOI: 10.1021/acsnano.0c04145

Chalcogenide phase-change materials show strikingly contrasting optical and electrical properties, which has led to their extensive implementation in various memory devices. By performing spin-, time-, and angle-resolved photoemission spectroscopy combined with the first-principles calculation, we report the experimental results that the crystalline phase of GeSb2Te4 is topologically nontrivial in the vicinity of the Dirac semimetal phase. The resulting linearly dispersive bulk Dirac-like bands that cross the Fermi level and are thus responsible for conductivity in the stable crystalline phase of GeSb2Te4 can be viewed as a 3D analogue of graphene. Our finding provides us with the possibility of realizing inertia-free Dirac currents in phase-change materials.

Tkachenko I.M., Kovalchuk A.I., Kobzar Y.L., Shekera O.V., Shevchenko V.V., Kurioz Y.I., Tereshchenko O.G., Nazarenko V.G. Optical properties of azo-based poly(azomethine)s with aromatic fluorinated fragments, ether linkages and aliphatic units in the backbone // Molecular Crystals and Liquid Crystals. 2020. Т. 697. № 1. С. 85-96. DOI: 10.1080/15421406.2020.1731080

The aim of this work is to study the optical properties of the core-fluorinated azo-containing polyazomethines with 1,4-tetrafluorobenzene or 4,4′-octafluorobiphenylene dioxyphenylene units and aliphatic fragments in the chain. Due to the reorganization process at the nanometer-scale under UV/Vis irradiation, azo-containing polymers (APs) have attracted much attention as materials for biology, optoelectronics, nano-manipulation field, etc. Moreover, the introduction of azomethine group into these polymers enhances not only their optical properties but also expands their practical application. APs polymers have the useful combination of chemical and physical properties such as liquid crystalline states, high nonlinearity and an ability to form metal complexes. It was shown that the optical properties of such polymers could be improved by the inclusion of fluorine. Fluorinated polymers demonstrate high thermal stability and have low dielectric constant and dielectric losses. It should be noted that the presence of flexible moieties in a polymer backbone allows regulating the different properties (solubility, thermostability, optical and liquid crystalline properties) of the final materials.

Zhevstovskikh I.V., Sarychev M.N., Averkiev N.S., Semenova O.I., Golyashov V.A., Tereshchenko O.E. Correlation of elastic and optoelectronic properties near structural phase transition in organic-inorganic lead iodide perovskite single crystals // Journal of Physics: Condensed Matter. 2020. Т. 33. № 4. С. 045403. DOI: 10.1088/1361-648X/abb9bb

The experimental evidence of the influence of the structural phase transition on the elastic and optoelectronic properties of CH3NH3PbI3 single crystals has been reported. A peak in the attenuation for longitudinal and shear ultrasonic waves and a step-like anomaly in their velocity have been found near the structural the orthorhombic-to-tetragonal phase transition (160 K). The narrow hysteresis observed in the temperature dependences of the elastic properties confirms that this is the first-order phase transition. A redshift of the absorption threshold (of about 110 meV) has been revealed both in the photocurrent (PC) and in the photoluminescence (PL) spectra with increasing temperature from 140 to 160 K. In the orthorhombic phase of CH3NH3PbI3 single crystals, the fine exciton structure in the PC spectrum has been found with an exciton binding energy of 19-25 meV. The peculiarities of the PC and PL spectra near the phase transition temperature (160 K) have been observed within a wider temperature range in contrast to the elastic anomalies that can be explained by the complex structure of the near-surface region. It may be essential for the further development of optoelectronic devices based on hybrid halide perovskites.