Magneto transport study of spin effects in two-dimensional indium arsenide systems
Beringer, Thomas W.
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Magneto transport data of four InAs/Al x Ga 1-x Sb quantum wells are presented. A surface pinning of the chemical potential, as well as growth related asymmetries at the interfaces, are expected to induce asymmetries in the crystal and external potentials. However, the expected beating pattern in the longitudinal resistance, a characteristic of spin-orbit coupling effects in asymmetric structures was not observed in any of the samples. No clear mechanism for this suppression is known. From analysis of the longitudinal resistance, the carrier density, mobility and effective masses are determined. By tilting the sample surface with respect to the magnetic field, the ratio of the Zeeman energy splitting to the Landau level separation changed. An effective g-factor of | g *| [approximate] 7 was estimated for a high mobility sample. Another quantum well sample shows a peak in conductivity at zero magnetic field. This is the signature of weak anti localization (WAL). Besides a beating pattern in ρ xx , WAL is an indication for the presence of spin-orbit coupling. With a metal gate fabricated as part of an MIS structure on one sample, the carrier density can be changed by about 15%. Carrier densities were measured from the period of SdH oscillations at different gate voltages. A large increase in the conductivity at zero magnetic field which can not be explained in the picture of WAL led to a further investigation of the conduction mechanism of a high mobility sample. Temperature dependence of the resistance indicate two dimensional variable range hopping conduction. This explains the feature observed in the conductivity.