赝形InGaAs/InAlAs渐变异质结中的零磁场自旋分裂

在赝形渐变InGaAs/In_0.52Al_0.48As异质结的二维电子气中,发现了自旋方向向上的电子和自旋向下的电子在零磁场下存在着自旋分裂.利用Shubnikov-de Haas振荡研究了异质结中的自旋分裂行为,通过振荡中的拍频现象,发现了零磁场下的自旋分裂量为8.76meV. 关键词：     

Quantum oscillations in p-type inversion layers of (111) and (100) silicon field effect transistors

For the first time Shubnikov-de Haas oscillations have been observed in p-type inversion layers of (111) and (100) silicon field effect transistors. For both orientations a single electric subband was found. The effective mass of the surface carriers was determined from the temperature dependence of the oscillations, for (111) surfaces as a function of the surface electric field. At low gate voltages spin splitting of the Landau levels was resolved.     

Semiclassical theory of transport in antidot lattices

Motivated by a recent experiment by Weiss et al. [Phys. Rev. Lett. 70, 4118 (1993)], we present a detailed study of quantum transport in large antidot arrays whose classical dynamics is chaotic. We calculate the longitudinal and Hall conductivities semiclassically starting from the Kubo formula. The leading contribution reproduces the classical conductivity. In addition, we find oscillatory quantum corrections to the classical conductivity which are given in terms of the periodic orbits of the system. These periodic-orbit contributions provide a consistent explanation of the quantum oscillations in the magnetoconductivity observed by Weiss et al. We find that the phase of the oscillations with Fermi energy and magnetic field is given by the classical action of the periodic orbit. The amplitude is determined by the stability and the velocity correlations of the orbit. The amplitude also decreases exponentially with temperature on the scale of the inverse orbit traversal time/T . The Zeeman splitting leads to beating of the amplitude with magnetic field. We also present an analogous semiclassical derivation of Shubnikov-de Haas oscillations where the corresponding classical motion is integrable. We show that the quantum oscillations in antidot lattices and the Shubnikov-de Haas oscillations are closely related. Observation of both effects requires that the elastic and inelastic scattering lengths be larger than the lengths of the relevant periodic orbits. The amplitude of the quantum oscillations in antidot lattices is of a higher power in Planck's constant and hence smaller than that of Shubnikov-de Haas oscillations. In this sense, the quantum oscillations in the conductivity are a sensitive probe of chaos.This paper is dedicated to Prof. H. Wagner on the occasion of his 60th birthday     

Shubnikov-de Haas oscillations in NbSe3

We have measured the resistivity of the linear transition metal trichalco-genide NbSe₃ in magnetic fields up to 180 kG. We observe large Shubnikov-de Haas oscillations. The measurements reveal a strong anisotropy in the a.c. plane perpendicular to the chain direction. A ratio of 3 in the cyclotron effective masses for the two orthogonal directions in this plane is determined. Spin splitting occurs for high magnetic field, and we obtain a Landé factor g of 2.45.     

Transport phenomena in low and high magnetic field (Shubnikov-de haas effect) in n-type Ga1−xAlxSb alloys

Galvanomagnetic measurements have been performed on n-type Ga_1?xAl_xSb with $\text{x ? 0.3}$. For the first time the Shubnikov-de Haas oscillations have been observed. The Г band contribution to the conductivity for x < 0.15 was clearly pointed out from the measurements of the periods of oscillations and Hall effect. The conduction effective mass at the Fermi level was deduced for several samples.     

Shubnikov-de Haas oscillations in p-type inversion layers on n-type silicon

Surface Shubnikov-de Haas oscillations have been measured in p-type channels of (110) silicon field effect transitors between 1.4 and 4.2 K in magnetic fields up to 10 Tesla. Two electric subbands were revealed and the effective masses of the holes in both bands could be determined. For one subband the dependence of the mass on the surface electric field was investigated. At low gate voltages the g-factor of the holes was measured from the spin splitting of the Landau-levels.     

Quantum oscillations in an inversion layer on p-PbTe

We report the observation of a variable density inversion layer on p-PbTe. The carriers in the inversion channel are found to have a mobility on the order of 250,000 cm² V^-1 sec^-1. Shubnikov-de Haas oscillations in the channel conductivity were measured in magnetic fields up to 6 T. From the observed periodicity we conclude that the oscillations represent only a fraction of the total number of electrons in the channel.     

Shubnikov-de Haas oscillations in n-channel silicon 〈100〉 MOSFETS in magnetic fields up to 35 T

Shubnikov-de Haas oscillations have been studied in n-channel silicon 〈100〉 MOSFETS in magnetic fields up to 35 T. At high magnetic fields the shape of the conductivity peaks becomes asymmetric and the conductivity from whole regions of the Landau level spectrum is suppressed by the magnetic field. The asymmetry is thought to arise from the low effective density of scatterers which occurs for high magnetic fields, as predicted by Ando. These effects may also be related to the presence of phenomena such as Wigner crystallisation or Anderson localisation.     

On the lowering of the electronic energy in model insulators due to surface reconstruction

Shubnikov-de Haas oscillations, piezoresistance, Hall mobility, and transverse “Hall” field due to mobility anisotropy have been studied on n-channel (111) Si inversion layers. The valley degeneracy was found to be 2 between 1.7 and 300 K. Under uniaxial mechanical stress the initially isotropic conductivity became strongly anisotropic. All results can be described by the existence of domains in the inversion layer.     

Comparison of Shubnikov-de Haas effect and cyclotron resonance on Si(100) MOS transistors under uniaxial stress

The stress induced population of the non-equivalent subbands E₀ to E′₀ is investigated by measurements of the magnetoconductivity — the Shubnikov-de Haas oscillations — and the cyclotron resonance taken on the same MOS transistor under identical conditions. In cyclotron resonance with increasing stress, a gradual transfer of carriers from E₀ to E′₀ is observed, whereas the Shubnikov-de Haas periodicity is unaffected and always yields a valley degeneracy of two. A domain model is required to resolve this apparent discrepancy.     

Oscillations quantiques des coefficients de pouvoir thermoelectrique et de conductivite thermique: theorie et mesures dans Cd3As2

Quantum oscillations have been observed in the thermoelectric power and thermal conductivity coefficients of a semiconductor Cd₃As₂ single crystal. Theoretical expressions for these coefficients, taking into account the Landau level broadening, are derived in this paper. The good agreement found between the thermoelectric power measurements and the corresponding theoretical expressions for the temperature and magnetic field dependence of the quantum oscillation amplitudes and the absolute values of the amplitudes has allowed us to calculate effective mass values which are in agreement with Shubnikov-de Haas measurements.     

Effect of the spin-orbit interaction on the cyclotron resonance of two-dimensional electrons

In the cyclotron resonance (CR) spectra of two-dimensional (2D) electrons in InAs quantum wells, the CR line splitting is observed. The splitting is found to be an oscillating function of magnetic field. The oscillations do not correlate with the filling factor. The experimental results are interpreted in terms of the spin-orbit splitting in the presence of a built-in electric field appearing due to the asymmetry of the quantum-well potential. From the splitting of the CR line, the spin-orbit coupling constant α_so is determined. The resulting value agrees well with the value obtained for the same sample from the Shubnikov-de Haas oscillations. The role of the resonance interaction of charge carriers in the well with the interface donor states is discussed.     

Hall effect plateaus and giant Shubnikov-de Haas oscillations in (BiSb)Telayered single crystals near the quantum limit

On bulk layered single crystals (Bi_0.25Sb_0.75)₂Te₃ with a hole concentration cm^-3 and a mobility cm²/Vs magnetoresistance and Hall effect investigations were performed in the temperature range T = 1.4 K ... 20 K in magnetic fields up to 18 T. For the magnetic field perpendicular to the layered structure giant Shubnikov-de Haas oscillations are measured; the positions of the maxima are triplets in the reciprocally scaled magnetic field. From the damping of the amplitudes with increasing temperature the cyclotron mass m _c = 0.12m ₀ is evaluated. Correlated with the SdH oscillations doublets of Hall effect plateaus (or kinks in low fields) are found. The weak well known Shubnikov-de Haas oscillations from the generally accepted multivallied highest valence band can be detected as a modulation on the giant oscillation. The high anisotropy of the SdH oscillations and their triplet structure in connection with the layered crystal structure lead us to suggest that the effects are caused by hole carrier pairing (mediated by the bipolaron mechanism) in quasi 2D sheets parallel to the crystal layer stacks. The measured Hall plateau resistances coincide with the quantum Hall effect values considering the number of layer stacks and the valley degeneracy of the 3D hole carrier reservoir. The ratio of spin splitting to Landau (cyclotron) splitting is observed to be . Received: 12 September 1997 / Revised: 8 January 1998 / Accepted: 22 January 1998     

Quantum oscillations in heavily doped bismuth chalcogenides

The observation of Shubnikov-de Haas and Hall oscillations in high-quality Bi_{2 ? x} Cu _x Se₃ single crystals is reported. Measurements carried out upon rotating the samples with respect to the magnetic field demonstrate that the oscillations originate from two-dimensional surface states in three-dimensional single crystals and are determined only by the perpendicular component of the magnetic field.     

Shubnikov-de haas effect in n-CdSnAs2

Shubnikov-de Haas oscillations in the transverse magnetoresistance of single-crystalline n-type CdSnAs₂ have been recorded at temperatures between 2 and 25 K in magnetic fields up to 5T. The electron concentration of the samples ranged from 2 × 10¹⁷ to 2 × 10¹⁸ cm^?3. The angular dependences of the oscillation periods and cyclotron effective masses showed that the conduction band exhibits an energy dependent anisotropy, obeying the Kildal band structure model. For the low-temperature values of the band parameters we found: a band gap E_g = 0.30 eV, a spin-orbit splitting Δ = 0.50 eV, a crystal field splitting parameter δ = ?0.09 eV, and an interband matrix element P = 8.5 × 10^?8eV cm. This simple four-level model was found to be not adequate to describe quantitatively the observed electronic effective g-factor for a sample with low electron concentration.     

Quantum corrections to the conductivity and periodic orbits: Integrable systems

We extend the recently developed semiclassical theory for the conductivity to periodic semiconductor structures whose classical dynamics is integrable. We find that the conductivity of integrable systems exhibits quantum oscillations as function of magnetic field and Fermi energy which are closely related to both the Shubnikov-de Haas oscillations and the oscillations observed in the conductivity of antidot lattices. A general expression for the quantum oscillations is derived which is analogous to the Berry-Tabor formula for the spectral density of integrable systems.     

Spin effects on oscillatory magnetoresistances in CdxHg1−xTe

A study is made of spin effects on the Shubnikov-de Haas oscillations in Cd_xHg_1?xTe alloys. The difference between the longitudinal and transverse magnetoresistances can be interpreted in terms of the spin-orbit couplings.     

Fermi surface in the new organic quasi-two-dimensional metal α-(BETS)2TlHg(SeCN)4

Quantum oscillations of de Haas-van Alphen and Shubnikov-de Haas and semiclassical angular oscillations of the magnetoresistance have been observed in the quasi-two-dimensional organic metal α-(BETS)₂TlHg(SeCN)₄. The quantum oscillations are connected with the cylindrical part of the Fermi surface. The angular oscillations are associated with the carrier motion on both the cylindrical part and quasi-planar sheets of the Fermi surface. The values of the Dingle temperature, T _D ≈ 2–3 K, and the effective mass, m* ≈ 1.03m ₀, have been defined. The possibility of the weakening of multibody interactions has been shown in this compound.     

Temperature dependence of hybrid quantum oscillations

The temperature dependence of the hybrid quantum oscillation amplitude in an accumulation layer on n-InAs is interpreted by analogy to the Shubnikov-de Haas effect. Amplitudes for oscillations corresponding to excited subbands follow the expected decay law. Characteristic decay energies, on the order of 5 meV, are compared to known intersubband spacings.