Квантовый размерный эффект и осцилляции Шубникова–де Гааза в поперечном магнитном поле в полупроводниковых нитях Bi0,92Sb0,08

The transport properties, magnetoresistance, and Shubnikov–de Haas (SdH) oscillations of glass-coated Bi0.92Sb0.08 single-crystal wires with diameters of 180 nm to 2.2 mm and the (1011) orientation along the wire axis, which are prepared by liquid phase casting, have been studied. For the first time, it has been found that the energy gap DE increases by a factor of 4 with a decrease in the wire diameter d owing to the manifestation of the quantum size effect. This significant increase in the energy gap can occur under conditions of an energy–momentum linear dispersion relation, which is characteristic of both the gapless state and the surface states of a topological insulator. It has been shown that, in a strong magnetic field at low temperatures, a semiconductor–semimetal transition occurs; it is evident in the temperature dependences of resistance in a magnetic field. An analysis of the SdH oscillations, namely, the phase shift of the Landau levels and the features of the angular dependences of the oscillation periods, suggests that the combination of the manifestation of the topological insulator properties and the quantum size effect leads to the occurrence of new effects in low-dimensional structures, which requires new scientific approaches and applications in microelectronics

Two-Dimensional Surface Topological Nanolayers and Dirac Fermions in Single Crystals of the Diluted Magnetic Semiconductor (Cd1−x−yZnxMny)3As2 (x + y = 0.3)

Features in the transverse magnetoresistance of single-crystalline diluted magnetic semiconductors of a (Cd1−x−yZnxMny)3As2 system with x + y = 0.3 have been found and analyzed in detail. Two groups of samples have been examined. The samples of the first group were thermally annealed for a long time, whereas the samples of the second group were not thermally annealed. The Shubnikov–de Haas (SdH) oscillations were observed for both groups of the samples within a 4.2 ÷ 30 K temperature range and under transverse magnetic field sweeping from 0 up to 11 T. The value of a phase shift, according to the SdH oscillations, was found to be a characteristic of the Berry phase existing in all the samples, except the unannealed sample with y = 0.08. Thickness of 2D surface topological nanolayers for all the samples was estimated. The thickness substantially depended on Mn concentration. The experimental dependence of reduced cyclotron mass on the Fermi wave vector, extracted from the SdH oscillations for the samples with different doping levels, is in satisfactory agreement with the predicted theoretical linear dependence. The existence of the Dirac fermions in all the samples studied (except the unannealed sample with y = 0.08) can be concluded from this result.

Influence of doping by tin, tallium and copper on quantum mobility of holes in antimony telluride single crystals

In this work we report the results of the extraction of quantum mobilty μq of holes from the Shubnikov – de Haas (SdH) effect at T = 4.2 K in single crystals Sb2–xSnxTe3 (x = 0.0; 0.005; 0.0075; 0.01); Sb2–xTlxTe3 (x = 0.0; 0.005; 0.015; 0.05) and Sb2–xCuxTe3(x = 0.0; 0.01; 0.03; 0.05; 0.07; 0.10), samples synthesized by the Bridgman method. Tl exhibits donor properties in Sb2Te3 while Sn and Cu show an acceptor behavior. Quantum mobility of holes, evaluated from SdH oscillations, decreases under doping in Sn doped samples about two times, in Tl doped samples about three times and in Cu doped samples less than two times at maximal Cu content x = 0.1. At the same time maximal Cu doping is 6 times (as compared with Sn) and 2 times (as compared with Tl) more. All measurements were made to Orient the magnetic field along the C3 axis. In this case, for the six-ellipsoid surface of Fermi light holes, all sections of ellipsoids coincide, and only one oscillation frequency is observed.

Quantum effects in electrical transport properties of Bismuth chalcogenides Topological Insulators

Quantum effects such as weak-antilocalisation (WAL) behavior and Shubnikov-de Haas (SdH) oscillations in the electrical transport properties of topological insulators, measured on nanostructured polycrystalline samples and single-crystals of a series of bismuth chalcogenide compounds (Bi2(SexTe1-x)3, 0 ≤ x ≤ 1 and BiSbTe3), are presented and discussed.

Quantum oscillations of robust topological surface states up to 50 K in thick bulk-insulating topological insulator

As personal electronic devices increasingly rely on cloud computing for energy-intensive calculations, the power consumption associated with the information revolution is rapidly becoming an important environmental issue. Several approaches have been proposed to construct electronic devices with low-energy consumption. Among these, the low-dissipation surface states of topological insulators (TIs) are widely employed. To develop TI-based devices, a key factor is the maximum temperature at which the Dirac surface states dominate the transport behavior. Here, we employ Shubnikov-de Haas oscillations (SdH) as a means to study the surface state survival temperature in a high-quality vanadium doped Bi1.08Sn0.02Sb0.9Te2S single crystal system. The temperature and angle dependence of the SdH show that: (1) crystals with different vanadium (V) doping levels are insulating in the 3–300 K region; (2) the SdH oscillations show two-dimensional behavior, indicating that the oscillations arise from the pure surface states; and (3) at 50 K, the V0.04 single crystals (Vx:Bi1.08-xSn0.02Sb0.9Te2S, where x = 0.04) still show clear sign of SdH oscillations, which demonstrate that the surface dominant transport behavior can survive above 50 K. The robust surface states in our V doped single crystal systems provide an ideal platform to study the Dirac fermions and their interaction with other materials above 50 K.

Электронная структура металлических слоев в двухслойном квазидвумерном органическом металле (BETS)-=SUB=-4-=/SUB=-HgBr-=SUB=-4-=/SUB=-(C-=SUB=-6-=/SUB=-H-=SUB=-4-=/SUB=-Cl-=SUB=-2-=/SUB=-)

We have studied the behavior of the Shubnikov–de Haas (SdH) oscillations in the quasi-two-dimensional dual-layered organic metal (BETS)_4HgBr_4(C_6H_4Cl_2). It is established that the spectrum of SdH oscillations in this compound agrees well with theoretical calculations and qualitatively coincides with the analogous spectrum of (ET)_4HgBr_4(C_6H_4Cl_2) isostructural organic metal. The fractional substitution of sulfur by selenium in the cationic layer strongly decreases the values of cyclotron masses. This decrease is most probably caused by weakening of the electron–phonon interaction.

Magneto – thermoelectric effects in quantum well in the presence of electromagnetic wave

We have studied magneto-thermoelectric effects in quantum well in the presence of electromagnetic wave. The analytic expression for Ettingshausen coefficient (EC) in the Quantum Well with parabolic potential (QWPP) in the presence of Electromagnetic wave (EMW) is calculated by using the quantum kinetic equation for electrons. The dependence of EC on the frequency, the amplitude of EMW, the Quantum Well parameters and the temperature are obtained. The results are numerically calculated, plotted, and discussed for GaAs/GaAsAl Quantum Well to clearly show the dependence of EC on above parameters and the results in this case are compared with the case in the bulk semiconductors. We realize that as the temperature increases, the EC decreases. The results show appearance of the Shubnikov–de Haas (SdH) oscillations when we survey the dependence of EC on the magnetic field. Keywords: Ettingshausen, Quantum well, Electromagnetic wave, parabolic potential, GaAs/GaAsAl.

Magnetotransport Investigations of Two-Dimensional Electron Gas for AlGaN/GaN Heterostructure

Magnetotransport properties are investigated in two-dimensional electron gas (2DEG) of AlGaN/GaN heterostructure, including the Drude conductance, the Shubnikov-de Haas (SdH) oscillations and the change with temperature, the electron-electron interaction (EEI) and the change with temperature, the weak antilocalization (WAL) and the change with temperature etc.

TRANSPORT IN A BILAYER SYSTEM AT HIGH LANDAU FILLING FACTOR

We have studied Shubnikov de Haas oscillations and the quantum Hall effect in GaAs -double well structures in tilted magnetic fields. We found strong magnetoresistance oscillations as a function of an in-plane magnetic field B∥ at ν = 4N + 3 and ν = 4N + 1 filling factors. At low perpendicular magnetic field B⊥, the amplitude of the conventional Shubnikov-de Haas (SdH) oscillations also exhibits B∥-periodic dependence at fixed values of B⊥. We interpret the observed oscillations as a manifestation of the interference between cyclotron orbits in different quantum wells.