-
Spin Orientation of Holes in Quantum Wells
Authors:
R. Winkler,
Dimitrie Culcer,
S. J. Papadakis,
B. Habib,
M. Shayegan
Abstract:
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 w…
▽ More
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.
△ Less
Submitted 11 November, 2008;
originally announced November 2008.
-
Anisotropic low-temperature piezoresistance in (311)A GaAs two-dimensional holes
Authors:
B. Habib,
J. Shabani,
E. P. De Poortere,
M. Shayegan,
R. Winkler
Abstract:
We 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 $1.6\times10^{11}$ cm$^{-2}$ and for a strain of about…
▽ More
We 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 $1.6\times10^{11}$ cm$^{-2}$ and for a strain of about $2\times10^{-4}$ applied along [01$\bar{1}$], e.g., the resistance measured along this direction changes by nearly a factor of two while the resistance change in the [$\bar{2}$33] direction is less than 10% and has the opposite sign. Our 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.
△ Less
Submitted 5 June, 2007;
originally announced June 2007.
-
Strong Aharonov-Bohm oscillations in GaAs two-dimensional holes
Authors:
B. Habib,
E. Tutuc,
M. Shayegan
Abstract:
We measured 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. In addition we observe resistance oscillations as a function of front gate bias at zero magnetic field. We discuss the results in light of spi…
▽ More
We measured 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. In addition we observe resistance oscillations as a function of front gate bias at zero magnetic field. We discuss the results in light of spin interference in the ring and possible applications to spintronics.
△ Less
Submitted 6 March, 2007; v1 submitted 27 December, 2006;
originally announced December 2006.
-
Tuning of the spin-orbit interaction in two-dimensional GaAs holes via strain
Authors:
B. Habib,
J. Shabani,
E. P. De Poortere,
M. Shayegan,
R. Winkler
Abstract:
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 2 x 10^{-4} strain.…
▽ More
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 2 x 10^{-4} strain. The results are in very good agreement with our numerical calculations of the strain-induced spin-splitting.
△ Less
Submitted 4 October, 2006;
originally announced October 2006.
-
Dephasing Time of Two-Dimensional Holes in GaAs Open Quantum Dots
Authors:
S. Faniel,
B. Hackens,
A. Vlad,
L. Moldovan,
C. Gustin,
B. Habib,
S. Melinte,
M. Shayegan,
V. Bayot
Abstract:
We report magnetotransport measurements of two-dimensional holes in open quantum dots, patterned either as a single-dot or an array of dots, on a GaAs quantum well. For temperatures $T$ below 500 mK, we observe signatures of coherent transport, namely, conductance fluctuations and weak antilocalization.
From these effects, the hole dephasing time $τ_φ$ is extracted using the random matrix theo…
▽ More
We report magnetotransport measurements of two-dimensional holes in open quantum dots, patterned either as a single-dot or an array of dots, on a GaAs quantum well. For temperatures $T$ below 500 mK, we observe signatures of coherent transport, namely, conductance fluctuations and weak antilocalization.
From these effects, the hole dephasing time $τ_φ$ is extracted using the random matrix theory. While $τ_φ$ shows a $T$-dependence that lies between $T^{-1}$ and $T^{-2}$, similar to that reported for electrons, its value is found to be approximately one order of magnitude smaller.
△ Less
Submitted 26 September, 2006;
originally announced September 2006.
-
Quantized conductance in an AlAs 2D electron system quantum point contact
Authors:
O. Gunawan,
B. Habib,
E. P. De Poortere,
M. Shayegan
Abstract:
We report experimental results on a quantum point contact (QPC) device formed in a wide AlAs quantum well where the two-dimensional electrons occupy two in-plane valleys with elliptical Fermi contours. To probe the closely-spaced, one-dimensional electric subbands, we fabricated a point contact device defined by shallow-etching and a top gate that covers the entire device. The conductance versus…
▽ More
We report experimental results on a quantum point contact (QPC) device formed in a wide AlAs quantum well where the two-dimensional electrons occupy two in-plane valleys with elliptical Fermi contours. To probe the closely-spaced, one-dimensional electric subbands, we fabricated a point contact device defined by shallow-etching and a top gate that covers the entire device. The conductance versus top gate bias trace shows a series of weak plateaus at integer multiples of $2e^2/h$, indicating a broken valley degeneracy in the QPC and implying the potential use of QPC as a simple "valley filter" device. A model is presented to describe the quantized energy levels and the role of the in-plane valleys in the transport. We also observe a well-developed conductance plateau near $0.7x2e^2/h$ which may reflect the strong electron-electron interaction in the system.
△ Less
Submitted 11 June, 2006;
originally announced June 2006.
-
Negative differential Rashba effect in two-dimensional hole systems
Authors:
B. Habib,
E. Tutuc,
S. Melinte,
M. Shayegan,
D. Wasserman,
S. A. Lyon,
R. Winkler
Abstract:
We demonstrate experimentally and theoretically that two-dimensional (2D) heavy hole systems in single heterostructures exhibit a \emph{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…
▽ More
We demonstrate experimentally and theoretically that two-dimensional (2D) heavy hole systems in single heterostructures exhibit a \emph{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.
△ Less
Submitted 14 September, 2004;
originally announced September 2004.
-
Spin Splitting in GaAs (100) Two-Dimensional Holes
Authors:
B. Habib,
E. Tutuc,
S. Melinte,
M. Shayegan,
D. Wasserman,
S. A. Lyon,
R. Winkler
Abstract:
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 $f_-$ and $f_+$, that correspond to the hole densities of the two spin subbands and a peak, at frequency $f_\mathrm{tot}$, corresponding to the total hole density. In addit…
▽ More
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 $f_-$ and $f_+$, that correspond to the hole densities of the two spin subbands and a peak, at frequency $f_\mathrm{tot}$, corresponding to the total hole density. In addition, the spectrum exhibits an anomalous peak at $f_\mathrm{tot}/2$. We also determined the effective masses of the two spin subbands by finding the inverse transform of the Fourier spectrum in the vicinity of $f_-$ and $f_+$, 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.
△ Less
Submitted 14 September, 2004;
originally announced September 2004.