Search

The results of the study of the influence of Cu on the Shubnikov–de Haas effect and the electrical properties of p-Sb2 –xCuxTe3 single crystals (0 ≤ x ≤ 0.1) are presented. In the framework of the parabolic model of the energy spectrum, the hole concentrations and the Fermi energy in Sb2 –xCuxTe3 are calculated based on the oscillation frequencies of the magnetoresistance. It is shown that doping by Cu has an acceptor effect and significantly increases the frequencies of Shubnikov–de Haas oscillations. A plateau is observed in the dependences of the Hall resistance on magnetic field. The dependences of the resistance on temperature obey the power law with the exponent m = 1.2, which is characteristic of scattering on phonons with the contribution of scattering on ionized impurities. Unlike other impurities, the exponent remains almost unchanged when doped by Cu to the maximum concentrations studied.

We have used the envelope function formalism to investigate the bands structure of LWIR type II SL InAs (d1 = 2. 18d2)/In0.25Ga0.75Sb(d2 = 21.5 Å). Thus, we extracted optical and transport parameters as the band gap, cut off wavelength, carriers effective mass, Fermi level and the density of state. Our results show that the higher optical cut-off wavelength can be achieved with smaller layer thicknesses. The semiconductor-semi metal transition was studied as a function of temperature. Our results permit us the interpretations of Hall and Shubnikov-de Haas effects. These results are in agreement with experimental results in literature and a guide for engineering infrared detectors.

Heterostructures with a GaAs/InGaAs/GaAs quantum well and aMn magnetic impurity layer separated from it, which have different conductivity types, are studied. At a Mn content not exceeding the amount corresponding to 0.5 monolayer of MnAs, a percolation cluster formed in the quantum well plane is not simply connected, but consists of metal drops separated by low-conductivity interspaces. Despite the absence of the simply connected conducting channel, Shubnikov–de Haas oscillations are observed in all studied systems, which are controlled by carrier properties in conducting drops, independent of Mn content. The estimate of drop sizes corresponds to theoretical values.

Quantum oscillations of the anomalous component of Hall resistance with an amplitude exceeding the amplitude of the Shubnikov-de Haas oscillations of transverse magnetoresistance are observed in mercury selenide crystals doped with low concentrations of cobalt impurity. In accordance with the predictions of the Hall effect theory for systems with spontaneous spin polarization of hybridized donor electrons, the observed oscillations correspond to magnetic quantum oscillations caused by the thermodynamic anomalous Hall effect.

We present magnetoresistance studies of the quasi-two-dimensional organic conductor $\kappa$-(BETS)$_2$Mn[N(CN)$_2$]$_3$, where BETS stands for bis\-(ethylene\-dithio)\-tetra\-selena\-fulvalene. Under a moderate pressure of 1.4\,kbar, required for stabilizing the metallic ground state, Shubnikov - de Haas oscillations, associated with a classical and a magnetic-breakdown cyclotron orbits on the cylindrical Fermi surface, have been found at fields above 10\,T. The effective cyclotron masses evaluated from the temperature dependence of the oscillation amplitudes reveal strong renormalization due to many-body interactions. The analysis of the relative strength of the oscillations corresponding to the different orbits and its dependence on magnetic field suggests an enhanced role of electron-electron interactions on flat parts of the Fermi surface., Comment: 6 pages, 4 figures

The results of experimental studies of the Shubnikov-de Haas (SdH) effect in the (013)-HgTe/Hg1-xCdxTe quantum wells (QWs) of electron type of conductivity both with normal and inverted energy spectrum are reported. Comprehensive analysis of the SdH oscillations measured for the different orientations of magnetic field relative to the quantum well plane and crystallographic exes allows us to investigate the anisotropy of the Zeeman effect. For the QWs with inverted spectrum, it has been shown that the ratio of the spin splitting to the orbital one is strongly dependent not only on the orientation of the magnetic field relative to the QW plane but also on the orientation of the in-plane magnetic field component relative to crystallographic axes laying in the QW plane that implies the strong anisotropy of in-plane g-factor. In the QW with normal spectrum, this ratio strongly depends on the angle between the magnetic field and the normal to the QW plane and reveals a very slight anisotropy in the QW plane. To interpret the data, the Landau levels in the tilted magnetic field are calculated within the framework of four-band kP model. It is shown that the experimental results can be quantitatively described only with taking into account the interface inversion asymmetry. © 2020 American Physical Society. We are grateful to E. L. Ivchneko for useful discussions. The work has been supported in part by the Russian Foundation for Basic Research (Grant No. 18-02-00050), by Act 211 Government of the Russian Federation, Agreement No. 02.A03.21.0006, by the Ministry of Science and Higher Education of the Russian Federation under Project No. FEUZ-2020-0054, and by the FASO of Russia (theme “Electron” No. 01201463326).

We present detailed studies of the high-field magnetoresistance of the layered organic metal κ-(BETS)2Mn- [N(CN)2]3 under a pressure slightly above the insulator-metal transition. The experimental data are analyzed in terms of the Fermi surface properties and compared with the results of first-principles band structure calculations. The calculated size and shape of the in-plane Fermi surface are in very good agreement with those derived from Shubnikov-de Haas oscillations as well as the classical angle-dependent magnetoresistance oscillations. A comparison of the experimentally obtained effective cyclotron masses with the calculated band masses reveals electron correlations significantly dependent on the electron momentum. The momentum- or band-dependent mobility is also reflected in the behavior of the classical magnetoresistance anisotropy in a magnetic field parallel to layers. Other characteristics of the conducting system related to interlayer charge transfer and scattering mechanisms are discussed based on the experimental data. Besides the known high-field effects associated with the Fermi surface geometry, new pronounced features have been found in the angle-dependent magnetoresistance, which might be caused by coupling of the metallic charge transport to a magnetic instability in proximity to the metal-insulator phase boundary., We are grateful to N.D. Kushch for providing the high-quality crystals for our studies and to P.D. Grigoriev for numerous useful discussions. The work was supported by the German Research Foundation (DFG) via the Grant No. KA 1652/4-1. The high-field measurements were done under support of the LNCMI-CNRS, member of the European Magnetic Field Laboratory (EMFL). V.N.Z. acknowledges the support from RFBR Grant No. 18-02-00280. Work in Spain was supported by the Spanish Ministerio de Economa y Competitividad (Grants No. FIS2015-64886-C5-4-P and No. CTQ2015-64579-C3-3-P) and Generalitat de Catalunya (2017SGR1506, 2017SGR1289, and XRQTC). E.C. acknowledges support from the Severo Ochoa Centers of Excellence Program under Grant No. SEV-2015-0496. P.A. acknowledges support from the Maria de Maeztu Units of Excellence Program under Grant No. MDM-2017-0767.

It is demonstrated that the copper-doped high-quality Bi Se single crystals with a high density of bulk charge carriers are certainly 3D topological insulators. The analysis of quantum Shubnikov−de Haas (SdH) oscillations reveals that these materials simultaneously exhibit two types of such oscillations determined by the Landau levels related to both the 3D and 2D Fermi surfaces.

A review of experimental and theoretical studies of transport phenomena in strongly anisotropic organic conductors is presented. Considerable attention is paid to the phenomena that are specific to quasi-2D and quasi-1D conductive structures and have no analogues both in ordinary metals and in truly 2D or 1D conducting systems. Angular magnetoresistance oscillations, de Haas–van Alphen and Shubnikov–de Haas phenomena, high-temperature quantum oscillations of the magnetoresistance, and high-frequency resonances, including those arising due to the motion of electrons open trajectories, are discussed. The resonant angular oscillations of high-frequency conductivity and weakly damped electromagnetic waves in quasi-2D organic conductors under strong spatial dispersion are considered.

The behavior of de Haas–van Alfven (dHvA) and Shubnikov–de Haas (ShdH) quantum oscillations in dual-layered quasi-two-dimensional organic metal (ET)4HgBr4(C6H4Cl2) is investigated. The oscillation spectra qualitatively agree with theoretical calculations of the bandgap structure. The angular dependence of the oscillation amplitude of magnetoresistance contains “spin zeros”; the analysis of the location of these zeros allows one to evaluate the electron–phonon interaction constant: λ ≈ 0.2.

Spin–orbit interaction effects are of great interest, primarily for the ability to modulate spin transport in a semiconductor channel for device applications. In particular, the Rashba spin–orbit (S–O) interaction allows for a tuneable spin modulation response dependent on the applied electric field, which can be achieved using standard semiconductor gate technology. We present evidence of the Rashba S–O interaction in two modulation doped germanium (Ge) quantum well (QW) heterostructures with different layer structures, and consequently different band structures and internal electric fields across the QW region. We show that two complementary low temperature magnetotransport analyses can be used to identify and quantify the Rashba S–O parameter in these materials, although quantification is limited in one case due to significant parallel conduction. We highlight that both techniques (Weak Antilocalisation and Shubnikov de-Haas oscillations) should be used when analysing a new material system as other conduction and magnetoresistive effects can obscure evidence of the Rashba S–O interaction in one or both of these regimes.

Features in the transverse magnetoresistance of single-crystalline diluted magnetic semiconductors of a (Cd1&ndash, x&ndash, 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&ndash, de Haas (SdH) oscillations were observed for both groups of the samples within a 4.2 &divide, 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.

We report on beating appearance in Shubnikov-de Haas oscillations in conduction band of 18-22nm HgTe quantum wells under applied top-gate voltage. Analysis of the beatings reveals two electron concentrations at the Fermi level arising due to Rashba-like spin splitting of the first conduction subband H1. The difference dN_s in two concentrations as a function of the gate voltage is qualitatively explained by a proposed toy electrostatic model involving the surface states localized at quantum well interfaces. Experimental values of dN_s are also in a good quantitative agreement with self-consistent calculations of Poisson and Schrodinger equations with eight-band kp Hamiltonian. Our results clearly demonstrate that the large spin splitting of the first conduction subband is caused by surface nature of $H1$ states hybridized with the heavy-hole band., 7 pages, 7 figures

Transport measurements at liquid helium temperatures were done on a number of Bi2Te2Se samples with thicknesses ranging from 30 to 200 μm in order to detect surface states. In each sample we observed Shubnikov–de Haas (SdH) oscillations and sublinear dependence of off-diagonal component of magnetoresistance tensor on magnetic field. The periods of SdH oscillations in inverse magnetic field were found to be the same within 15%. The positions of SdH oscillations are determined by the normal to surface component of magnetic field. We found that the measured conductivity can be well described by a model with two groups of electrons, 2D and 3D. The conductivity of 2D electrons was found to be relatively weakly varying from sample to sample and not depending on thickness in a systematic manner. This behavior can be explained only by their localization on the surface. Comparison of the results of magnetotransport measurements with our scanning tunneling spectroscopy results on atomically smooth Bi2Te2Se surface in ultrahigh vacuum led us to conclude that the surface electrons are separated from the bulk electrons by a depletion layer approximately 100 nm thick. This effect could provide the dominant contribution of surface electrons to conductivity in samples with thicknesses less than 200 nm.

HEMT structures with In0.53Ga0.47As quantum well are synthesized using molecular-beam epitaxy on InP substrates. The structures are double-side Si δ-doped so that two dimensionally-quantized subbands are occupied. The effect of the central InAs nanoinsert in the quantum well on the electron effective masses m* and mobilities in each subband is studied. For experimental determination of m*, the quantum μ q and transport μ t mobilities of the two-dimensional electron gas in each dimensionally-quantized subband, the Shubnikov-de Haas effect is measured at two temperatures of 4.2 and 8.4 K. The electron effective masses are determined by the temperature dependence of the oscillation amplitudes, separating the oscillations of each dimensionally-quantized subband. The Fourier spectra of oscillations are used to determine the electron mobilities μ q and μ t in each dimensionally-quantized subband. It is shown that m* decreases as the InAs-nanoinsert thickness d in the In0.53Ga0.47As quantum well and electron mobilities increase. The maximum electron mobility is observed at the insert thickness d = 3.4 nm.

Quantum Hall Effect In an external magnetic field, the energy of an electron in a two-dimensional system takes discrete values, called Landau levels. At high enough fields, all electrons in a solid can fit in the lowest Landau level. If exactly half of that level is filled with electrons, standard

We have performed two-dimensional Fourier transform spectroscopy on intrinsic and modulation doped quantum wells in external magnetic fields up to 10 T. In the undoped sample, the strong Coulomb interactions and the increasing separations of the electron and hole charge distributions with increasing magnetic fields lead to a nontrivial in-plane dispersion of the magneto-excitons. Thus, the discrete and degenerate Landau levels are coupled to a continuum. The signature of this continuum is the emergence of elongated spectral line shapes at the Landau level energies, which are exposed by the multidimensional nature of our technique. Surprisingly, the elongation of the peaks is completely absent in the lowest Landau level spectra obtained from the modulation doped quantum well at high fields.

The fractional quantum Hall effect (FQHE) in two-dimensional electron system (2DES) is an exotic, superfluid-like matter with an emergent topological order. From the consideration of Aharonov-Bohm interaction of electrons and magnetic field, the ground state of a half-filled lowest Landau level is mathematically transformed to a Fermi sea of composite objects of electrons bound to two flux quanta, termed composite fermions (CFs). A strong support for the CF theories comes from experimental confirmation of the predicted Fermi surface at $\nu$ = 1/2 (where $\nu$ is the Landau level filling factor) from the detection of the Fermi wave vector in the semi-classical geometrical resonance experiments. Recent developments in the theory of CFs have led to a prediction of a $\pi$ Berry phase for the CF circling around the Fermi surface at half-filling. In this paper we provide the first experimental evidence for the detection of the Berry phase of CFs in the fractional quantum Hall effect. Our measurements of the Shubnikov-de Haas oscillations of CFs as a function carrier density at a fixed magnetic field provide a strong support for an existence of a $\pi$ Berry phase at $\nu$ = 1/2. We also discover that the conductivity of composite fermions at $\nu$ = 1/2 displays an anomalous linear density dependence, whose origin remains mysterious yet tantalizing., Comment: accepted to Nature Physics

Kinetics of intrasubband energy relaxation of electrons in the system of Landau levels lying below the optical phonon energy is studied. Extraordinary behavior of the relaxation of electronic subsystem excitation energy is detected. Despite the fact that its main channel is optical phonon emission, the total relaxation time exceeds the characteristic times of scattering on optical phonons by several orders of magnitude.

The carrier distribution over Landau levels was studied in resonant tunneling GaAs/AlGaAs quantum well structures under tunneling pumping of the upper subband. The numerical calculations of the Landau levels population for various values of pumping intensity (tunneling time), magnetic field and the structure doping were carried out. The effect of various scattering mechanisms, as two-electron (electron–electron scattering) as single-electron (acoustic phonon and interface roughness scattering) ones on level population was studied. The population inversion between the zeroth Landau level of the upper subband and the first Landau level of the lowest subband was shown to exist in wide range of the magnetic field strength thus providing the possibility of wide range tunable stimulated terahertz emission.

The carrier distribution over Landau levels was studied in resonant tunneling GaAs/AlGaAs quantum well structures under tunneling pumping of the upper subband. The numerical calculations of the Landau level populations for various values of pumping intensity (tunneling time), magnetic field and structure doping were carried out. The population inversion between zeroth Landau level of the upper subband and the first Landau level of the lowest subband was shown to exist in wide range of the magnetic field strength. The effect of various scattering mechanisms, both two-particle (electron-electron scattering) and single-particle (acoustic phonon and interface roughness scattering) ones, on level population was studied. The way of lifting the selection rule forbidding the inter-Landau level terahertz transitions of interest and achieving considerable values of the dipole matrix element is proposed.

The influence of the width of the quantum well L and doping on the band structure, scattering, and electron mobility in nanoheterostructures with an isomorphic In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum well grown on an InP substrate are investigated. The quantum and transport mobilities of electrons in the dimensionally quantized subbands are determined using Shubnikov-de Haas effect measurements. These mobilities are also calculated for the case of ionized-impurity scattering taking into account intersub-band electron transitions. It is shown that ionized-impurity scattering is the dominant mechanism of electron scattering. At temperatures T < 170 K, persistent photoconductivity is observed, which is explained by the spatial separation of photoexcited charge carriers.

Quantization of Hall resistivity in strongly correlated two-dimensional electronic systems at high magnetic fields generally indicates the stabilization of novel electronic quantum liquid phases of matter. This is the nature of the integer and fractional quantum Hall states that stabilize at integer and fractional odd-denominator (not always, though) filling factors of the Landau level. Away from certain filling factors that represent quantum Hall liquid states, different phases, some of them with unusually high magneto-transport anisotropy have been known to stabilize specially in high Landau levels. In this work, we try to understand this anisotropic behaviour in terms of effective electron-electron interaction potentials. To this effect, we implement a full projection of the original Coulomb interaction potential in the suitable Landau level. We find out that, in high Landau levels, thus for relatively weak magnetic fields, a semi-classical description of the interaction potential between electrons appear to be an adequate choice. The features of this semi-classical interaction potential in this limit suggest ways how the energetic balance between density waves and/or liquid crystalline phases might be sensitively affected.

The influence of the doping level, illumination, and width of isomorphic In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum wells grown on InP substrates on the electron mobility is studied. The persistent photoconductivity at low temperatures is found. Band diagrams are calculated and optimal parameters are found for obtaining the maximum electron mobility. The quantum and transport electron mobilities in dimensional quantization subbands are obtained from the Shubnikov-de Haas effect. The electron mobilities are calculated in dimensional quantization subbands upon scattering by ionized impurities taking intersubband transitions into account. Scattering by ionized impurities in samples studied is shown to be dominant at low temperatures.

The temperature dependence of the Shubnikov–de Haas oscillations of longitudinal magnetoresistance of a two-dimensional electron system with the Rashba spin-orbit interaction is analyzed by using the expression for conductivity derived by S. G. Novokshonov and A. G. Groshev, Phys. Rev. B 74, 245333 (2006). It is shown that in the above system there exist magneto-intersubband oscillations of the kinetic coefficients characteristic for multisubband conductors. The period of these oscillations is determined by the spin precession frequency at the Fermi level ΩBF. In the case under consideration, the intersubband spin splitting depends on electron energy. This results in a weak temperature dependence of the magneto-intersubband oscillation amplitude, which is determined by Λ* = (2π2kBT/ℏωc)ℏ ΩBF / eF. This dependence is considerably weaker in comparison to the temperature smoothing of the Shubnikov–de Haas oscillation amplitude due to a small parameter (ℏ ΩBF /eF ≪ 1).

We report in this Rapid Communication an antilevitation behavior of Landau levels in vanishing magnetic fields in a high quality heterojunction insulated-gated field-effect transistor. We found, in the Landau fan diagram of electron density versus magnetic field, the positions of the magnetoresistance minima at Landau-level fillings $\ensuremath{\nu}=4\ensuremath{-}6$ move below the ``traditional'' Landau-level line to lower electron densities. Moreover, the even and odd filling factors show quantitatively different behaviors in antilevitation, suggesting that the exchange interactions may be important.

Compressively strained Ge quantum well devices have a spin-splitting in applied magnetic field that is entirely consistent with a Zeeman effect in the heavy hole valence band. The spin orientation is determined by the biaxial strain in the quantum well with the relaxed SiGe buffer layers and is quantized in the growth direction perpendicular to the conducting channel. The measured spin-splitting in the resistivity ρxx agrees with the predictions of the Zeeman Hamiltonian where the Shubnikov-deHaas effect exhibits a loss of even filling factor minima in the resistivity ρxx with hole depletion from a gate field, increasing disorder or increasing temperature. There is no measurable Rashba spin-orbit coupling irrespective of the structural inversion asymmetry of the confining potential in low p-doped or undoped Ge quantum wells from a density of 6 × 1010 cm−2 in depletion mode to 1.7 × 1011 cm−2 in enhancement.

We report the first picosecond time-resolved photoluminescence measurementsof hot-carrier relaxation in a modulation-doped GaAs-GaAlAs MQW in the presence of strong magnetic fields. We have measured the lifetimes of carriers in excited Landau levels and have determined the time-dependent carrier temperature. We find that the cooling rate is slower in applied field tthan at B=0; also there is a significant increase in the cooling rate for B {greater-than or approximate} 10T. We report also the observation of highly time-dependent linewidths of the Landau levels. © 1985.

A review is made of the quantum effects which are observed in the transport coefficients of semiconductors. Quantization of the free carriers in semiconductors is produced whenever an external pote...

We report a study of the quantum Hall effect and Shubnikov-dc Haas oscillations in semimctallic type II heterostructures of the strained layer system InAs/Ga1−xInxSb which are almost intrinsic. In high magnetic fields up to 50 T, ρxy has large peaks, demonstrating the high degree of charge compensation in the system. Between these peaks, intrinsic quantum Hall minima arc observed, where ρxy approaches zero.

Electron energy loss rates have been studied from the amplitude of Shubnikov-de Haas oscillations at temperatures between 500 mk and 10 K. At small magnetic fields there is a considerable enhancement of the loss rate which the authors interpret as evidence for 'cyclotron phonon' emission. When this mechanism is not dominating, they deduce an electron acoustic phonon scattering rate of 3*108 T s-1 K-1.

Transport properties of the complex oxide LaAlO3/SrTiO3 interface are investigated under high magnetic field (55T). By rotating the sample with respect to the magnetic field, the two-dimensional nature of charge transport is clearly established. Small oscillations of the agnetoresistance with altered periodicity are observed when plotted versus inverse magnetic field. We attribute this effect to Rashba spin-orbit coupling which remains consistent with large negative magnetoresistance when the field is parallel to the sample plane. A large inconsistency between the carrier density extracted from Shubnikov-de Haas analysis and from the Hall effect is explained by the contribution to transport of at least two bands with different mobility., Comment: 5 pages, 3 figures

We investigate the competition between electron-solid and quantum-liquid phases in graphene, which arise in partially filled Landau levels. The differences in the wave function describing the electrons in the presence of a perpendicular magnetic field in graphene with respect to the conventional semiconductors, such as GaAs, can be captured in a form factor which carries the Landau level index. This leads to a quantitative difference in the electron-solid and -liquid energies. For the lowest Landau level, there is no difference in the wave function of relativistic and non-relativistic systems. We compute the cohesive energy of the solid phase analytically using a Hartree-Fock Hamiltonian. The liquid energies are computed analytically as well as numerically, using exact diagonalization. We find that the liquid phase dominates in the n=1 Landau level, whereas the Wigner crystal and electron-bubble phases become more prominent in the n=2 and n=3 Landau level., Comment: 11 pages, 7 figures

We report on a prototype device geometry where a number of quantum point contacts are connected in series in a single quasi-ballistic InAs nanowire. At finite magnetic field the backscattering length is increased up to the micron-scale and the quantum point contacts are connected adiabatically. Hence, several input gates can control the outcome of a ballistic logic operation. The absence of backscattering is explained in terms of selective population of spatially separated edge channels. Evidence is provided by regular Aharonov–Bohm-type conductance oscillations in transverse magnetic fields, in agreement with magnetoconductance calculations. The observation of the Shubnikov–de Haas effect at large magnetic fields corroborates the existence of spatially separated edge channels and provides a new means for nanowire characterization.

The use of Shubnikov-de Haas oscillations for determining effective mass is illustrated by a study of the magnetotransport properties of the two-dimensional hole gas in Si1− x Ge x (x = 0.13, 0.36, 0.95, 0.98) quantum wells. For some samples the data cannot be fitted to standard theoretical curves in which the scattering of charge carriers is described by the conventional Dingle factor. The reasons for the discrepancies between the experiment the theory are: (i) the effect of spin splitting on the amplitude of the peak in the SdH oscillations; (ii) extra broadening of the Landau levels attributable to an inhomogeneous distribution of the carrier concentration; (iii) the coexistence of short and long-range scattering potentials; and, (iv) population of the second energy level in the quantum well. Ways of calculating the effective hole masses m* for all these cases are presented and values of m* are found for the heterostructures studied here.

The paper is concerned with the theoretical and experimental studies of the band structure and electrical properties of InAlAs/InGaAs/InAlAs/InP heterostructures containing a composite InGaAs quantum well with InAs and GaAs nanoinserts. From the Shubnikov-de Haas effect, the effective cyclotron mass m * is determined experimentally and calculated with consideration for the nonparabolicity of the electron energy spectrum. An approach to estimation of the effective mass is proposed and tested. The approach is based on weighted averaging of the m * of the composite quantum well’s constituent materials. A first proposed heterostructure containing two InAs inserts symmetrically arranged in the quantum well makes a 26% reduction in m * compared to m * in the lattice-matched In0.53Ga0.47As quantum well possible.

We study the Landau level broadening by analyzing the Shubnikov-de Haas oscillations in a gated AlGaAs/GaAs parabolic quantum well structure when only one electronic subband is occupied. Small-angle scattering is determined to be important in this system. The Shubnikov-de Haas oscillations are described equally well by employing Gaussian or Lorentzian broadening of the Landau levels at low magnetic field where the quantum localization effect is not important. A possible explanation is that the electron–electron interactions lead to the overlapping of adjacent Landau levels and one can not distinguish between the two broadening types.

The magnetic torque and magnetoresistance of the quasi-two-dimensional charge transfer salt β″-(ET)4(H3O)[Fe(C2O4)3] · C6H4Cl2 have been investigated in pulsed magnetic fields of up to 55 T. As opposed to de Haas–van Alphen oscillations, Shubnikov–de Haas oscillations are observed up to temperatures as high as 32 K at ambient pressure despite significant thermal damping in the low-temperature range. This feature, which is also observed under applied pressure, is interpreted in terms of the coexistence of a closed orbit and a quantum interference path with the same cross section.

In X Ga 1− X Sb has the highest hole mobility amongst all III–V semiconductors which can be enhanced further with the use of strain. The use of confinement and strain in In X Ga 1− X Sb quantum wells lifts the degeneracy between the light and heavy hole bands which leads to reduction in the hole effective mass in the lowest occupied band and an increase in the mobility. We present magnetotransport measurements on compressively strained In X Ga 1− X Sb and GaSb quantum wells. Hall-bar and Van de Pauw structures were fabricated and Shubnikov–de Haas oscillations in the temperature range of T = 2–10 K for magnetic fields of B = 0–9 T were measured. The reduction of effective hole mass with strain was quantified. These results are in excellent agreement with modeling results from band structure calculations of the effective hole mass in the presence of strain and confinement.

A new mechanism of creating the population inversion in the system of Landau levels in resonance-tunneling multiple quantum-well structures has been proposed. It has been shown that when the distance between the lower subbands is smaller than the energy of an optical phonon (i.e., when the scattering by optical phonons is suppressed), the population of the ground (zeroth) Landau level of the upper subband can be substantially higher than the population of the first Landau level of the lowest subband, which opens the opportunity of obtaining the tunable-frequency generation of induced terahertz electromagnetic radiation at such a transition.

We report on an ultrahigh Hall mobility exceeding 40 000 cm2/V s and a very long traditional scattering time in a trivial layered semiconductor Bi2O2Se. Shubnikov-de Haas (SdH) oscillations were observed in both the unsaturated longitudinal linear magnetoresistance Rxx and the transverse Hall resistance Rxy. The amplitude ΔRxy of SdH oscillations was phase-shifted approximately 180° with respect to ΔRxx, indicating the strong suppression of electron backward scattering. This was further proved by the evidence of transport lifetime that is 10 times longer than the quantum lifetime. Our results show that the suppressed backward scattering in nontrivial Dirac semimetals can also occur in the trivial semiconductor Bi2O2Se.

The magneto-transport properties of Bi2Se3–ySy were investigated. Magnetoresistance (MR) decreases with an increase in the S content, and finally, for 7% (i.e., y = 0.21) S doping, the magnetoresistance becomes negative. This negative MR is unusual as it is observed when a magnetic field is applied in the perpendicular direction to the plane of the sample. The magneto-transport behavior shows the Shubnikov–de Haas (SdH) oscillation, indicating the coexistence of surface and bulk states. The negative MR has been attributed to the non-trivial bulk conduction.

Low-temperature magnetotransport studies are reported for (112)Cd3As2 films grown on (111)CdTe by molecular beam epitaxy as a function of the Cd3As2 film thickness. All films show Shubnikov-de Haas oscillations. An even-integer quantum Hall effect is observed for films thinner than 70 nm. For the thinnest films, the bulk is gapped and transport at low temperatures occurs only via the gapless, two-dimensional states. The lowest Landau level is reached at ∼10 T, and the longitudinal resistance nearly vanishes at the plateaus in the Hall resistance. The results are discussed in the context of the current theoretical understanding of topological surface states in three-dimensional Dirac semimetals.

We report the density and magnetic field dependence of the valley splitting of two-dimensional electrons in (100) Si metal–oxide–semiconductor field-effect transistors, as determined via activation measurements in the quantum Hall regime. We find that the valley activation gap can be greatly enhanced at high magnetic fields as compared to the bare valley splitting. The observation of strong dependence of the valley activation gap on orbital Landau level occupancy and similar behavior of nearby spin gaps suggest that electron–electron interactions play a large role in the observed enhancement.

Broadening of the Landau levels in graphene and the associated quantum Hall plateau-to-plateau transition are investigated numerically. For correlated bond disorder, the graphene-specific n = 0 Landau level of the Dirac fermions becomes anomalously sharp accompanied by the Hall transition exhibiting a fixed-point-like criticality. Similarly anomalous behavior for the n = 0 Landau level is also shown to occur in correlated random magnetic fields, which suggests that the anomaly is generic to disorders that preserve the chiral symmetry.

The subband structure and occupation in the triangular quantum well at Al x Ga1−x N/GaN heterointerfaces have been investigated by means of temperature dependent Shubnikov–de Haas (SdH) measurements at low temperatures and high magnetic fields under illumination. After the illumination of the heterostructures, the total two-dimensional electron gas concentration increases, and the SdH oscillation amplitudes are enhanced when there is no additional subband occupation. It is also found that the energy separation between the subbands decreases after the illumination. We suggest that the illumination decreases the electric field and thus weakens the quantum confinement of the triangular quantum well at Al x Ga1−x N/GaN heterointerfaces. The GaN layer is thought to be the primary contributor of the excited electrons by the illumination.

Temperature dependence of the longitudinal magnetoresistance has been measured for bismuth single crystals doped with a small amount of antimony (0.1, 0.3, 0.6, 1.0, 1.5 and 2.3 at%) up to 5 T of magnetic field in the temperature range between 1.2 and 23 K. The amplitude of longitudinal Shubnikov–de Haas (SdH) oscillations for the doped samples is markedly enhanced with decreasing temperature in spite of the Landau level broadening. To understand this anomaly, a simple numerical simulation is made for studying how the oscillation amplitude is affected by the temperature as well as impurity. This simulation supports the fact that the increase in the number of scattering centers and the lower value of damping factor of the SdH oscillation due to impurity-doping lead to the large amplitude at lower temperatures. The Dingle term became dominant at higher temperatures.

The beating pattern of Shubnikov-de Haas oscillations in 2D electron system in the presence of a Rashba zero-field spin splitting is reproduced. It is shown, taking into account the Zeeman splitting, that the explicit formulae for the node position well describes the experimental data. The spin-orbit interaction strength obtained is found to be magnetic field independent in an agreement with the basic assumptions of the Rashba model., Comment: 4 pages, 2 figures

Four-terminal magnetotransport measurements have been performed on a mesoscopic graphite wire with a thickness of about seven graphene layers in which the carrier density can be tuned via the field effect using a back gate and in-plane gates. The conductance measured as a function of back gate voltage and temperature can be well described by the simple two-band model. Measurements of Shubnikov–de Haas oscillations agree well with the parameters extracted at zero magnetic field with the help of the model. Measurements of the weak localization correction to the conductivity and conductance fluctuations confirm the mesoscopic character of electronic transport and allow to estimate the phase-coherence length to be of the order of the wire length (several microns) at the lowest temperatures. The results are compatible with electron–electron interactions being responsible for decoherence at the lowest temperatures.

We examine the variation of the amplitude of Shubnikov–de Haas (SdH) oscillations under the influence of photoexcitation in the regime of the radiation-induced zero-resistance states in GaAs/AlGaAs devices. We find that the SdH amplitude scales linearly with the average background resistance in the vicinity of the radiation-induced resistance minima. The results show that the SdH amplitude vanishes in proportion to the background resistance at the centers of the zero-resistance states.