Quantum transport in one-dimensional GaAs hole systems (original) (raw)
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Ballistic hole transport and the 0.7 anomaly in p-type GaAs quantum wires
2008
K.-Studying the spin degree of freedom of charge carriers in semiconductors is an area of significant current interest. Although spin-orbit coupling is extremely strong in p-type semiconductors such as GaAs, to date there have been only a limited number of experiments on holes in p-GaAs nanostructures. We have fabricated extremely high quality 1D hole quantum wires that show up to 10 extremely clean and stable quantized conductance plateaus at B=0 [1]. In contrast to 1D electrons, we observe an extreme anisotropy of the Zeeman spin splitting of the 1D energy levels depending on whether the magnetic field is parallel or perpendicular to the quantum wire [2]. We use this anisotropy to show that the 0.7 feature and zero bias anomaly are both spin related in hole quantum wires [3]. [1] O.
0.7 Structure and zero bias anomaly in ballistic hole quantum wires
Physical Review Letters, 2008
We study the anomalous conductance plateau around G 0:72e 2 =h and the zero bias anomaly in ballistic hole quantum wires with respect to in-plane magnetic fields applied parallel B k and perpendicular B ? to the quantum wire. As seen in electron quantum wires, the magnetic fields shift the 0.7 structure down to G 0:52e 2 =h and simultaneously quench the zero bias anomaly. However, these effects are strongly dependent on the orientation of the magnetic field, owing to the highly anisotropic effective Landé g-factor g in hole quantum wires. Our results highlight the fundamental role that spin plays in both the 0.7 structure and zero bias anomaly.
Filtering spin with tunnel-coupled hole quantum wires
2003
Creating spin-polarized currents in nonmagnetic semiconductors is one of the key prerequisites for realizing spintronics devices. We have shown previously that the k-linear Rashba spin splitting present in two-dimensional (2D) electron systems can be utilized in a momentumselective tunneling geometry to design a spin filter without using magnetic fields or ferromagnetic contacts. Motivated by the fact that spin-orbit effects are typically much stronger in 2D hole systems, we consider quantum wires formed by additional confinement of the lowest (heavy-hole) 2D valence subband. Its k 3 -type Rashba term gives rise to a k-linear spin splitting for holes in the quantum wire. Implementation of the spin-filter design is then analogous to the electron case but, in the hole system, requires less momentum selectivity and should therefore be easier to realize.
Effect of gate-driven spin resonance on the conductance through a one-dimensional quantum wire
Physical Review B, 2013
We consider quasiballistic electron transmission in a one-dimensional quantum wire subject to both time-independent and periodic potentials of a finger gate that results in a coordinate-and time-dependent Rashba-type spin-orbit coupling. A spin dependent conductance is calculated as a function of external constant magnetic field, the electric field frequency, and potential strength. The results demonstrate the effect of the gate-driven electric dipole spin resonance in a transport phenomenon such as spin-flip electron transmission.
Conductance quantization and the 0.7�� 2e 2/h conductance anomaly in one-dimensional hole systems
2006
We have studied ballistic transport in a 1D channel formed using surface gate techniques on a back-gated, high-mobility, bilayer 2D hole system. At millikelvin temperatures, robust conductance quantization is observed in the quantum wire formed in the top layer of the bilayer system, without the gate instabilities that have hampered previous studies of 1D hole systems. Using source drain bias spectroscopy, we have measured the 1D subband spacings, which are 5-10 times smaller than in comparable GaAs electron systems, but 2-3 times larger than in previous studies of 1D holes. We also report the first observation of the anomalous conductance plateau at G = 0.7 × 2e 2 /h in a 1D hole system.
Spin polarization in modulation-doped GaAs quantum wires
We study spin polarization in a split-gate quantum wire focussing on the effect of a realistic smooth potential due to remote donors. Electron interaction and spin effects are included within the density functional theory in the local spin density approximation. We find that depending on the electron density, the spin polarization exhibits qualitatively different features. For the case of relatively high electron density, when the Fermi energy EF exceeds a characteristic strength of a long-range impurity potential V donors , the density spin polarization inside the wire is practically negligible and the wire conductance is spin-degenerate. When the density is decreased such that EF approaches V donors , the electron density and conductance quickly become spin polarized. With further decrease of the density the electrons are trapped inside the lakes (droplets) formed by the impurity potential and the wire conductance approaches the pinch-off regime. We discuss the limitations of DFT-LSDA in this regime and compare the obtained results with available experimental data.
Conductance quantization and the 0.7×2e[sup 2]∕h conductance anomaly in one-dimensional hole systems
Applied Physics Letters, 2006
We have studied ballistic transport in a 1D channel formed using surface gate techniques on a back-gated, high-mobility, bilayer 2D hole system. At millikelvin temperatures, robust conductance quantization is observed in the quantum wire formed in the top layer of the bilayer system, without the gate instabilities that have hampered previous studies of 1D hole systems.
Physical Review B, 2009
We present a detailed theoretical study of the electronic spectrum and Zeeman splitting in hole quantum wires. The spin-3/2 character of the topmost bulk-valence-band states results in a strong variation of subband-edge g factors between different subbands. We elucidate the interplay between quantum confinement and heavy-holelight-hole mixing and identify a certain robustness displayed by low-lying hole-wire subband edges with respect to changes in the shape or strength of the wire potential. The ability to address individual subband edges in, e.g., transport or optical experiments enables the study of holes states with nonstandard spin polarization, which do not exist in spin-1/2 systems. Changing the aspect ratio of hole wires with rectangular cross-section turns out to strongly affect the g factor of subband edges, providing an opportunity for versatile in-situ tuning of hole-spin properties with possible application in spintronics. The relative importance of cubic crystal symmetry is discussed, as well as the spin splitting away from zone-center subband edges. E k L=0 S=1/2 J = 3/2 z J = 1/2 z J = 1/2 z J=3/2 J=1/2 L=1 FIG. 1: (Color online) Schematic dispersion of bulk-semiconductor conduction and valence bands (solid lines).
Tunable Spin-Splitting and Spin-Resolved Ballistic Transport in GaAs/AlGaAs Two-Dimensional Holes
Physical Review Letters, 1998
We report quantitative experimental and theoretical results revealing the tunability of spin splitting in high-mobility two-dimensional GaAs hole systems, confined to either a square or a triangular quantum well, via the application of a surface-gate bias. The spin splitting depends on both the hole density and the symmetry of the confinement potential and is largest for the highest densities in asymmetric potentials. In the triangular well, when the spin splitting is sufficiently large, our measured commensurability oscillations, induced by a one-dimensional periodic potential, exhibit two frequencies providing clear evidence for spin-resolved ballistic transport. [S0031-9007(98)06750-7]