Weak-localization-like temperature-dependent conductivity of a dilute two-dimensional hole gas in a parallel magnetic field

We have studied the magnetotransport properties of a high mobility two-dimensional hole gas (2DHG) in a 10 nm GaAs quantum well with densities in the range of (0.7-1.6) x 10(10) cm(-2) on the metallic side of the zero-field "metal-insulator transition." In a parallel field well above B(c) that suppresses the metallic conductivity, the 2DHG exhibits a conductivity Delta(g)(T) approximately (1/pi) (e(2)/h)lnT reminiscent of weak localization for Fermi liquids. The experiments are consistent with the coexistence of two phases in our system: a metallic phase and a weakly insulating Fermi liquid phase.     

Wigner function of a two-dimensional electron gas in a magnetic field

The Wigner function of a two-dimensional electron gas in an arbitrary magnetic field perpendicular to the plane in which the electrons are confined is constructed rigorously. The function is useful in taking various statistical averages and illuminates the roles played by the hyperbolic functions of the field which appear in the expressions of the susceptibility and other physical quantities.     

Surface plasmon in a parallel magnetic field

Using a hydrodynamic model the dispersion relation for the surface plasmon is calculated in an external magnetic field parallel to the surface when the wave propagates perpendicular to the magnetic field. In the limit of zero wave vector, the results reduce to those of Chiu and Quinn who have used the dielectric constant in the local theory.     

Two-dimensional metal in a parallel magnetic field

We have investigated the effect of an in-plane parallel magnetic field (B(axially) on two high mobility metallic-like dilute two-dimensional hole gas systems in GaAs quantum wells. The experiments reveal that, while suppressing the magnitude of the low temperature resistance drop, B(axially) does not affect E(a), the characteristic energy scale of the metallic resistance drop. The field B(c) at which the metallic-like resistance drop vanishes is dependent on both the width of the quantum well and the orientation of B(axially). It is unexpected that E(a) is unaffected by B(axially) up to B(c) despite the fact that the Zeeman energy at B(c) is roughly equal to E(a).     

The Wigner crystal in a semimetal film in a high magnetic field

The possibility of existance of a super-crystalline (Wigner) phase in a semimetal or impurity semiconductor film placed in a high magnetic field, is discussed and a comparison is made with a crystal in a three-dimensional specimen.

Such a phase exists in a succession of magnetic field or particle density intervals. The vibrational spectrum depends on magnetic field, while the bind energy is only density-dependent. The mean-square displacement x² of the particles in the lattice sites are also independent on the magnetic field over a wide temperature range.     

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)     

Quantum limit in a parallel magnetic field in layered conductors

We show that electron wave functions in a quasi-two-dimensional conductor in a parallel magnetic field are always localized on conducting layers. In particular, wave functions and the electron spectrum in a quantum limit, where the sizes of quasiclassical electron orbits are of the order of nanoscale distances between the layers, are determined. ac infrared measurements to investigate Fermi surfaces and to test Fermi-liquid theory in quasi-two-dimensional organic and high-Tc materials in high magnetic fields, H approximately equal 10-45 T, are suggested.     

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.     

The thermal conductivity of polar gases in a magnetic field

Measurements are reported of the change in the thermal conductivity coefficients ?λ^∥ and ?λ^⊥ of polar gases under the influence of a magnetic field at room temperature. Investigated are the linear molecules HCl, DCl, HCN, OCS and CO₂ and the symmetric top molecules CH₃F, CD₃F, CH₃CN, CHF₃, NH₃ and ND₃. The results on the nonequilibrium polarizations WJ and W?JJ obtained from these experiment are expressed in terms of effective cross sections. With the present results the amount of data now available on certain effective cross sections has grown to an extent that justifies a systematic overview. Correlations are presented between the effective cross sections and various molecular properties such as the electric dipole moment and the moments of inertia.     

Doped graphene in a quantizing magnetic field: Hall conductivity

The energy spectrum of electrons in doped graphene corresponding to the Landau levels in an external transverse magnetic field has been calculated in the low-energy approximation. The magnetic-field dependence of the electrical conductivity has been determined based on the derived dispersion relation of electrons in the doped graphene. The behavior of the conductivity has been analyzed for different impurity parameters, such as the hybridization potential and energy of adsorbed atoms.     

Electrodynamic response of a quantum nanotube in a parallel magnetic field

This paper reports on a theoretical study of intraband resonances arising in the absorption of electromagnetic radiation by a quantum nanotube both with and without involvement of optical phonons. Explicit relations are derived for the absorption coefficients. The relative intensities of the resonance peaks are analyzed.     

Compressibility of a two-dimensional electron gas in a parallel magnetic field

The thermodynamic compressibility of a two-dimensional electron system in the presence of an in-plane magnetic field is calculated. We use accurate correlation energy results from quantum Monte Carlo simulations to construct the ground state energy and obtain the critical magnetic field B_c required to fully spin polarize the system. Inverse compressibility as a function of density shows a kink-like behavior in the presence of an applied magnetic field, which can be identified as B_c. Our calculations suggest an alternative approach to transport measurements of determining full spin polarization.     

Ballistic conductance of a quasi-one-dimensional microstructure in a parallel magnetic field

We discuss the behavior of the ballistic conductance of a quasi-one-dimensional microstructure in a parallel magnetic field when there is electron scattering by a single point impurity inside a channel. An exact analytic formula for the conductance is derived for a model in which the confinement potential is a parabolic well. We show that the conductance curve consists of quantization steps with sharp resonance peaks near the thresholds. Finally, we find the amplitudes and halfwidths of these peaks. Zh. éksp. Teor. Fiz. 111, 2215–2225 (June 1997)     

Magnetoresistance of a two-dimensional electron gas in a parallel magnetic field

The conductivity of a two-dimensional electron gas in a parallel magnetic field is calculated. We take into account the magnetic-field-induced spin-splitting, which changes the density of states, the Fermi momentum, and the screening behavior of the electron gas. For impurity scattering, we predict a positive magnetoresistance for low electron density and a negative magnetoresistance for high electron density. The theory is in qualitative agreement with recent experimental results found for Si inversion layers and Si quantum wells.