K. H. Gao

Transport properties of AlGaAs/GaAs parabolic quantum wells

We report on the magnetotransport properties of 100 nm wide parabolic quantum wells and observe an enhancement of the Hall resistance in one sample but not the other. This phenomenon is likely related to the effective thickness of the electronic slab. We also observe a parabolic negative magnetoresistance originating from electron-electron interactions when only one subband is occupied in one of the samples. The interaction correction to the Drude conductivity is extracted using two methods. We find that the extracted interaction correction increases with increasing tilted angle, for which two possible explanations are given.

Weak antilocalization and beating pattern in high electron mobility AlxGa1−xN/GaN two-dimensional electron gas with strong Rashba spin-orbit coupling

The weak antilocalization (WAL) effects of the two-dimensional electron gas (2DEG) in high mobility AlxGa1−xN/GaN heterostructure as well as beating patterns in the Shubnikov–de Haas (SdH) oscillatory magnetoresistance have been investigated by means of magnetotransport measurements before and after illumination. The zero-field spin splitting mainly arising from the Rashba spin-orbit coupling effect is studied using the weak antilocalization and beating patterns analysis, respectively. The Rashba spin-orbit coupling constant α deduced using the weak antilocalization analysis showed a good agreement with that estimated from the analysis of the beating patterns for the sample before and after illumination. For our sample, the electron motion in the high mobility system is in the ballistic regime, the experimental WAL curves were fitted by a simulated quantum conductance correction according to a model proposed by [Golub [Phys. Rev. B 71, 235310 (2005)].

Influence of the illumination on weak antilocalization in an AlxGa1−xN∕GaN heterostructure with strong spin-orbit coupling

The weak antilocalization effects of the two-dimensional electron gas in a high mobility AlxGa1−xN∕GaN heterostructure have been investigated by means of magnetotransport measurements before and after illumination. The zero-field spin splitting mainly arising from the Rashba spin-orbit coupling effect as a function of electron concentration as well as a function of temperature is studied using the weak antilocalization analysis. The Rashba spin-orbit coupling constant α deduced using the weak antilocalization analysis shows a rapid decrease with the increase of the measured electron concentration.

Transport properties of a spin-split two-dimensional electron gas in an In0.53Ga0.47As∕InP quantum well structure

We study the magnetotransport properties of a gated In0.53Ga0.47As∕InP quantum well structure in the presence of spin splitting when only one electronic subband is occupied. We develop an analytical method to extract the quantum mobilities for the two spin subbands. Ionized impurity scattering and alloy disorder scattering are determined to be important in this system. Larger quantum mobility is found for the higher-energy spin subband. We also demonstrate that the difference between the quantum mobilities for the two spin subbands can be altered with the gate.

Experimental approaches to zero-field spin splitting in a gated high-mobility In0.53Ga0.47As/InP quantum well structure: Weak antilocalization and beating pattern

We report on the strong spin-orbit (SO) interaction in a gated high-mobility In0.53Ga0.47As/InP quantum well two-dimensional electron gas. We establish that the SO interaction is dominated by the Rashba mechanism. The Rashba coupling parameters determined from analysis of both weak antilocalization and the beating pattern in the Shubnikov–de Haas oscillations are in reasonable agreement, and the small difference between them was explained by a magnetic-field-dependent effective g factor. The zero-field spin splitting shows nonmonotonic behavior with a maximum as the electron density is varied with the applied gate voltage. This is related to strong Rashba SO coupling in our sample.

Magnetoresistance in high-density two-dimensional electron gas confined in InAlAs/InGaAs quantum well

We study the magnetoresistance of a high-density two-dimensional electron gas confined in an InAlAs/InGaAs quantum well and observe a parabolic negative magnetoresistivity at moderate field. This negative magnetoresistivity is induced by electron-electron interactions. The interaction correction to the Drude conductance is extracted from the negative magnetoresistivity. However, due to inhomogeneity in the electron density, there is a contribution of positive magnetoresistivity, which induces the larger extracted correction than anticipated.

Microwave-enhanced dephasing time in a HgCdTe film

The antilocalization effect in a compensated HgCdTe film is observed. With an applied microwave field, both the zero-magnetic-field conductance and the dephasing time are enhanced nonlinearly with microwave power. The observation concerning the dephasing time is inconsistent with a heating mechanism. Such behavior is also in contrast to the microwave-induced suppression of weak-antilocalization and dephasing time seen for a two-dimensional electron gas of the anodic-oxidized HgCdTe. The nonlinear increase in zero-magnetic-field conductance is consistent with a microwave-assisted-hopping mechanism. The increased dephasing time can be explained qualitatively by the microwave-assisted-hopping mechanism and a microwave-induced increase in the electron density.

Strong Spin-Orbit Interactions in an InAlAs/InGaAs/InAlAs Two-Dimensional Electron Gas by Weak Antilocalization Analysis

Spin-orbit interactions in a two-dimensional electron gas were studied in an InAlAs/InGaAs/InAlAs quantum well. Since weak anti localization effects take place far beyond the diffusive regime, (i.e., the ratio of the characteristic magnetic field, at which the magnetoresistance correction maximum occurs, to the transport magnetic field is more than ten) the experimental data are examined by the Golub theory, which is applicable to both diffusive regime and ballistic regime. Satisfactory fitting lines to the experimental data have been achieved using the Golub theory. In the strong spin-orbit interaction two-dimensional electron gas system, the large spin splitting energy of 6.08 meV is observed mainly due to the high electron concentration in the quantum well. The temperature dependence of the phase-breaking rate is qualitatively in agreement with the theoretical predictions