B. Habib

Spin orientation of holes in quantum wells

This paper reviews the spin orientation of spin-3/2 holes in quantum wells. We discuss the Zeeman and Rashba spin splitting in hole systems that are qualitatively different from their counterparts in electron systems. We show how a systematic understanding of the unusual spin-dependent phenomena in hole systems can be gained using a multipole expansion of the spin density matrix. As an example we discuss spin precession in hole systems that can give rise to an alternating spin polarization. Finally, we discuss the qualitatively different regimes of hole spin polarization decay in clean and dirty samples.

Strong Aharonov-Bohm oscillations in GaAs two-dimensional holes

The authors measured Aharonov-Bohm resistance oscillations [Phys. Rev. 115, 485 (1959)] in a shallow two-dimensional GaAs hole ring structure, defined by local anodic surface oxidation. The amplitude of the oscillations is about 10% of the ring resistance, the strongest seen in a hole system. In addition the authors observe resistance oscillations as a function of front gate bias at zero magnetic field. They authors discuss the results in light of spin interference in the ring and possible applications to spintronics.

Spin–orbit interaction and transport in GaAs two-dimensional holes

We present quantitative measurements and calculations of the spin–orbit-induced zero magnetic field spin-splitting in GaAs two-dimensional hole systems. The magneto-resistance oscillations in this system show a clear beating pattern which results from the unequal densities of the two spin subbands. We present a Fourier analysis technique that de-convolves the magneto-oscillations of the two subbands. The temperature dependence of the de-convolved oscillations allows us to deduce the effective masses of the subbands without assuming parabolic dispersions for the two subbands. Next, we demonstrate that heavy hole systems in heterostructures exhibit a decrease in spin-splitting with an increase in perpendicular electric field. Our results are in contrast to the more familiar case of electrons where spin-splitting increases with electric field. Another external parameter that effects spin-splitting is strain. We report direct measurements of the spin–orbit interaction-induced spin-splitting in a hole system as a function of anisotropic, in-plane strain. In addition, our piezoresistance measurements reveal a strong dependence on density and the direction along which the resistance is measured. In the end, we present Aharonov–Bohm resistance oscillations in a shallow two-dimensional GaAs hole ring structure, defined by local anodic surface oxidation. The amplitude of the oscillations is about 10% of the ring resistance, the strongest seen in a hole system.

Negative differential Rashba effect in two-dimensional hole systems

We demonstrate experimentally and theoretically that two-dimensional s2Dd heavy-hole systems in single heterostructures exhibit a decrease in spin–orbit interaction-induced spin splitting with an increase in perpendicular electric field. Using front and back gates, we measure the spin splitting as a function of applied electric field while keeping the density constant. Our results are in contrast to the more familiar case of 2D electrons where spin splitting increases with electric field.

Spin splitting in GaAs (100) two-dimensional holes.

We measured Shubnikov–de Haas (SdH) oscillations in GaAs ~100! two-dimensional holes to determine the inversion asymmetry-induced spin splitting. The Fourier spectrum of the SdH oscillations contains two peaks, at frequencies f2 and f1 , that correspond to the hole densities of the two spin subbands and a peak, at frequency f tot , corresponding to the total hole density. In addition, the spectrum exhibits an anomalous peak at f tot/2. We also determined the effective masses of the two spin subbands by finding the inverse transform of the Fourier spectrum in the vicinity of f2 and f1 , and then analyzing the temperature dependence of the SdH oscillations for each subband. We discuss our results in light of self-consistent calculations and previous experiments.

Tuning of the spin-orbit interaction in two-dimensional GaAs holes via strain

We report direct measurements of the spin-orbit interaction-induced spin splitting in a modulation-doped GaAs two-dimensional hole system as a function of anisotropic, in-plane strain. The change in spin-subband densities reveals a remarkably strong dependence of the spin splitting on strain, with up to about 20% enhancement of the splitting upon the application of only about

Anisotropic low-temperature piezoresistance in (311)A GaAs two-dimensional holes

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Quantized conductance in an AlAs two-dimensional electron system quantum point contact

strain. The results are in very good agreement with our numerical calculations of the strain-induced spin splitting.

Dephasing time of two-dimensional holes in GaAs open quantum dots: Magnetotransport measurements.

The authors report low-temperature resistance measurements in a modulation-doped, (311)A GaAs two-dimensional hole system as a function of applied in-plane strain. The data reveal a strong but anisotropic piezoresistance whose magnitude depends on the density as well as the direction along which the resistance is measured. At a density of 1.6×1011cm−2 and for a strain of about 2×10−4 applied along the [011¯], e.g., the resistance measured along this direction changes by nearly a factor of 2, while the resistance change in the [2¯33] direction is less than 10% and has the opposite sign. The accurate energy band calculations indicate a pronounced and anisotropic deformation of the heavy-hole dispersion with strain, qualitatively consistent with the experimental data. The extremely anisotropic magnitude of the piezoresistance, however, lacks a quantitative explanation.