Two-dimensional electron-hole system in a HgTe-based quantum well

A two-dimensional electron-hole system consisting of light high-mobility electrons with a density of N _s = (4–7) × 10¹⁰ cm^?2 and a mobility of μ _n = (4–6) × 10⁵ cm²/V s and heavier low-mobility holes with a density of P _s = (0.7–1.6) × 10¹¹ cm^?2 and a mobility of μ _p = (3–7) × 10⁴ cm²/V s has been discovered in a quantum well based on mercury telluride with the (013) surface orientation. The system exhibits a number of specific magnetotransport properties in both the classical magnetotransport (positive magnetoresistance and alternating Hall effect) and the quantum Hall effect regime. These properties are associated with the coexistence of two-dimensional electrons and holes.     

Electrically induced luminescence in parabolic quantum wells in a magnetic field

Interband luminescence in a parabolic quantum well is studied in applied electric and magnetic fields. It is shown that the luminescence peak is displaced towards higher frequencies with increasing magnetic field strength, while an increase in the electric field strength causes a displacement of the emission peak towards the long-wave region and a decrease in its amplitude. The theoretical results are compared with the experimental data. The existence of a new electromagnetic-wave emission channel (electrically induced luminescence) associated with indirect optical transitions is predicted. The frequency dependence of the electrically induced radiation is computed, taking into account the interaction of an electron with acoustic and optical phonons. It is found that the half-width of the luminescence peak increases with the electric field strength.     

Two-dimensional quantum antiferromagnet in a strong magnetic field

The behaviour of the two-dimensional quantum antiferromagnet of arbitrary spin in a strong transversal magnetic field on a square lattice is studied in terms of the equivalent Bose gas problem. The existence of phase transition from the state characterized by “quasi-long-range” magnetic order to the disordered ferromagnetic state is demonstrated. The expressions for correlation functions, thermodynamical and magnetic characteristics are derived.     

System of quantum wells in a parallel magnetic field

The energy spectrum and quantum states of electrons in a system of quantum wells in a strong magnetic field parallel to the heterogeneous boundaries are studied. The combined effect of the quantizing magnetic field and the potential of the system of quantum wells leads to a radical change in the electron dispersion relation owing to the appearance of one-dimensional Landau bands. The neighborhoods of the anticrossing points of the different bands correspond to an effective redistribution of the electron envelope functions, which becomes stronger as the magnetic field is raised. The character of the electron-state density in the size-quantization subbands is examined qualitatively in connection with the change in the system of isoenergy contours when a magnetic field is applied. Fiz. Tverd. Tela (St. Petersburg) 40, 1719–1723 (September 1998)     

Exciton polaritons in quantum wells in a transverse magnetic field

Physics of the Solid State - This paper reports on a study of the exciton polariton region in reflection spectra of wide CdTe/CdZnTe quantum wells (with well width exceeding by far the exciton Bohr...     

Plasmons in double quantum wells in a parallel magnetic field

Collective intraband charge-density excitations in the quasi-two-dimensional electron system of double GaAs/AlGaAs quantum wells in an external parallel magnetic field B_∥ are studied by inelastic light scattering. It has been found that the energy of the excitations under study (acoustic and optical plasmons) exhibits anisotropy depending on the mutual orientation of B_∥ and the excitation quasi-momentum k. It is shown theoretically that, in a strong parallel magnetic field, the effects associated with the finite width of the quantum wells dominate over the effects associated with interlayer tunneling and determine the anisotropy of plasmons. The experimental data are compared with a theoretical calculation.     

Manifestation of a semimetallic state in cyclotron resonance in low-symmetry HgTe-based quantum wells

Cyclotron-resonance measurements in 21-nm-thick HgTe/CdHgTe quantum wells of different crystallographic orientations have been performed. It has been found that, in contrast to the structures with the (001) orientation of the quantum-well plane, (013)-oriented quantum wells are semimetallic and their absorption spectra exhibit both electron and hole cyclotron-resonance lines. The simultaneous presence of the two types of charge carriers originates from an overlap between the upper heavy-hole quantum-confinement subbands hh1 and hh2. This overlap is caused by the strong interaction of these subbands with the Dyakonov-Khaetskii interface state. Calculations carried out using the eight-band kp-Hamiltonian indicate that, for known values of the band-structure parameters, the overlap between hh2 and hh1 subbands does not occur; this result is in agreement with the cyclotron-resonance data for (001)-oriented structures. The enhanced interaction between heavy-hole and interface states owing to the existence of steps at low-symmetry heterointerfaces may be the mechanism responsible for the appearance of an overlap between subbands in HgTe quantum wells with orientation different from (001).     

Intrinsic spin hall effect induced by quantum phase transition in HgCdTe quantum wells

The spin Hall effect can be induced by both extrinsic impurity scattering and intrinsic spin-orbit coupling in the electronic structure. The HgTe/CdTe quantum well has a quantum phase transition where the electronic structure changes from normal to inverted. We show that the intrinsic spin Hall effect of the conduction band vanishes on the normal side, while it is finite on the inverted side. By tuning the Cd content, the well width, or the bias electric field across the quantum well, the intrinsic spin Hall effect can be switched on or off and tuned into resonance under experimentally accessible conditions.     

Two-dimensional Thomas-Fermi parabolic quantum dot in a weak magnetic field

The Thomas-Fermi equation, in conjunction with the Poisson equation is solved exactly for the problem of the two-dimensional circular parabolic quantum dot in the presence of a weak magnetic field, in the framework of the local spin-density approximation. The total energy, chemical potential, differential capacitance, degree of polarization, and diamagnetic susceptibility were calculated. Asymptotic solutions were obtained for the limits of strong and weak confinement. Received 19 February 1999 and Received in final form 26 July 1999     

Conductance of a quantum wire in a longitudinal magnetic field

We examine the ballistic conductance of a quantum wire in a parallel magnetic field in the presence of several impurities and derive analytic expressions for the transmission coefficient and the conductance in such a system. We show that scattering by impurities leads to a number of sharp peaks near the thresholds of the conductance quantization steps. The number of such peaks is determined by the distance between the impurities and the energy of the scattered particle. We also study the conductivity of a quantum wire in the region where the transport mechanism is diffusive. The conductivity is examined for the case in which charge carriers are scattered by randomly distributed point impurities. We study Shubnikov-de Haas oscillations in such a system. The general oscillation pattern consists of broad minima separated by irregularly spaced sharp peaks of the burst type. Zh. éksp. Teor. Fiz. 113, 1376–1396 (April 1998)     

Electron-LO-phonon interaction in wurtzite GaN quantum wells under a magnetic field

We calculate the electron-LO-phonon relaxation rates in wurtzite GaN quantum wells in the presence of a magnetic field parallel to the growth direction. Using the dielectric continuum model (DCM), we are able to include contributions from both the interface and the quasi-confined phonon modes. The relaxation rate expression takes the phonon dispersion into account, and is applicable to all phonon modes. We find that the relaxation rates show strong oscillations as a function of the applied magnetic field. In relatively wide (8 nm) quantum wells, the inclusion of interface phonon mode decreases this oscillation amplitude. But in thin wells (5 nm), the interface phonon mode is of the same importance as the quasi-confined mode, and it strongly modifies the oscillation behavior.     

Magnetic field induced transition in a quantum magnet described by the quantum dimer model

The effect of a magnetic field on a gapped quantum magnet is described within the framework of the quantum dimer model. A minimal model describing the proliferation of itinerant spinons above a critical field is proposed and investigated by Lanczos exact diagonalizations and quantum Monte Carlo simulations. For both square and triangular lattices, it is shown that spinons are fully polarized and Bose condense. This offers a novel scenario of a quantum critical point in the dimer-liquid phase (triangular lattice) characterized by the continuous appearance of a spinon superfluid density, contrasting with the usual triplet condensation picture. The possible role of other spinon kinetic terms neglected in the model are discussed.     

Resonant magnetopolaron effects in parabolic quantum wells in a tilted magnetic field

We study the resonant magnetopolaron effects in parabolic quantum wells in a tilted magnetic field. The renormalization of the first excited level, which is resonant with the ground state level plus one longitudinal-optical phonon is calculated at the resonance using an improved resonance approximation to be E= where is the polaron coupling constant. The exponent and the factor are calculated in dependence on the tilt angle of the magnetic field and the confinement energy.     

Two-dimensional electrons in spirally rolled-up quantum wells

An effective Hamiltonian is obtained to describe the motion of a one-dimensional quantum particle along an arbitrary plane curve. Calculations are made of the energy levels and the polarization dependence of the electromagnetic wave absorption in a spirally rolled-up quantum well.     

Effect of band mixing of the hole subbands in quantum wells on the optical transition intensities in a magnetic field

The results of interband magneto-optical measurements of GaAs quantum wells are compared with the calculated transition energies and amplitudes in a six-band envelope function approach. The evaluation of the transition matrix elements helps to explain all the essential features of the observed spectra and elucidate the complex effects of hole subbands mixing. Excitonic corrections are included in a simplified manner while a 11% larger value of the electron effective mass is needed to fit the experimental data.     

Negative effective mass induced by in-plane magnetic fields in n-doped wide quantum wells

By solving the coupled Schrödinger and Poisson's equations self-consistently, we have theoretically investigated the in-plane magnetic-field-induced negative effective mass (NEM) in n-doped wide quantum wells. The NEM originates from the interaction of Hartree potential and magnetic-field-introduced potential. Without n-type doping, no NEM section arises at any magnetic field densities. The value of NEM and the width of NEM section can be effectively adjusted by magnetic field, electrical field, and doping concentration, which make it possible to utilize the above system to realize the tunable terahertz source.     

Metal-insulator transition induced by the magnetic field in n-type GaSb

The metal-insulator (MI) transition induced by a magnetic field was evidenced for the first time in compensated n-type GaSb layers grown by molecular beam epitaxy. The free electron densities were in the low 10¹⁶ cm⁻³ range or even slightly lower, so that the zero-field 3D electron gas was degenerate and, at the B_MI magnetic field of the MI transition, it populates only the spin-split 0⁽⁺⁾ Landau level (extreme quantum limit). On the metallic side of the MI transition a T^1/3 dependence of the conductivity was assumed to fit the low-T data and to estimate the B_MI value, which resulted of 9.1 T in the purest sample. The MI transition manifests in a strong increase of the diagonal resistivity with the magnetic field, but not of the Hall coefficient, suggesting that the apparent electron density is practically constant, whereas the mobility varies strongly. The evidence of a maximum in the temperature dependence of the Hall coefficient has been explained through a two channels transport mechanism involving localized and extended states.     

Two-dimensional oscillator in a magnetic field

The energy and eigenstate spectrum of a charged particle in the electric field of a 2D anisotropic oscillator and in a uniform magnetic field is considered. The exact analytic solution to the problem is obtained for an arbitrary magnetic field strength. The characteristic features of variation of the energy spectrum depending on the magnetic field strength are analyzed. The results of this study are of interest for the quantum-mechanical theory of magnetism and can be used to simulate the magnetic properties of atoms and molecules.