Dimensional Hole System Research Articles

Landau level spin diode in a GaAs two dimensional hole system

We have fabricated and characterized a Landau level spin diode in a GaAs two-dimensional hole system. We used the spin diode to probe the hyperfine coupling between hole and nuclear spins and found no detectable net nuclear spin polarization, indicating that hole–nuclear spin flip-flop processes are suppressed by at least factor of 50 compared to GaAs electron systems.

Density inhomogeneity driven metal–insulator transition in 2D p-GaAs

In this work, we present a study of the temperature and carriers density dependence of the electrical transport of high mobility two dimensional hole system grown on the (311) surface of GaAs. At low temperatures, the analysis of the variation of conductivity data as σ(ps)∝(ps−psc⁎)δ shows that a density inhomogeneity in the metallic phase leading to percolation-type transition to an insulating state at a critical density psc⁎ that decrease slowly with increasing temperature and found to be lower than the corresponding estimate psc based on the sign of the slope dρ/dT. The experimental values of the exponent δexp are close to theoretical values corresponding to the 2D percolation transition (δth=4/3).

Magnetism in a Mn modulation-doped InAs/InGaAs heterostructure with a two-dimensional hole system

For an InAs quantum well which is modulation-doped with Mn we measure directly and simultaneously the magnetization and magnetic anisotropy of, both, the two dimensional hole system (2DHS) and Mn dopants. Using highly sensitive micromechanical torque magnetometry at 400 mK we observe the de Haas-van Alphen effect of the 2DHS in a magnetic field B up to 14 T. Around B=0 we find a magnetic hysteresis which we attribute to the spontaneous ordering of magnetic moments in the interacting Mn-hole system. Tilted field experiments suggest a uniaxial magnetic anisotropy with the easy axis in (001) growth direction.

Spin-Hall effect in two-dimensional mesoscopic hole systems

The spin Hall effect in two dimensional hole systems is studied by using the four-terminal Landauer-B\"{u}ttiker formula with the help of Green functions. The spin Hall effect exists even when there are {\em not} any correlations between the spin-up and -down heavy holes (light holes) and when the $\Gamma$-point degeneracy of the heavy hole and light hole bands is lifted by the confinement or recovered by the strain. When only a heavy hole charge current without any spin polarization is injected through one lead, under right choice of lead voltages, one can get a pure heavy (light) hole spin current, combined with a possible impure light (heavy) hole spin current from another two leads. The spin Hall coefficients of both heavy and light holes depend on the Fermi energy, devise size and the disorder strength. It is also shown that the spin Hall effect of two dimensional hole systems is much more robust than that of electron systems with the Rashba spin-orbit coupling and the spin Hall coefficients do not decrease with the system size but tend to some nonzero values when the disorder strength is smaller than some critical value.

BREAKDOWN OF THE QUANTUM HALL EFFECTS IN HOLE SYSTEMS AT HIGH INDUCED CURRENTS

The magnetisation of two dimensional hole systems in the quantum Hall regime has been studied using a highly-sensitive torsion balance magnetometer. In a time varying magnetic field eddy currents are induced which become large around integer and fractional filling factors where ρxx takes a very low value. The sweep rate and temperature dependence of these induced currents are in good agreement with the model of quantum Hall effect breakdown proposed recently by Matthews et al. This model also allows comparison between the energy gap at different filling factors and so provides a measurement of the fractional quantum Hall effect energy gap, Δ1/3, and the spin split energy gap, g*μ B B.

Confinement symmetry, mobility anisotropy, and metallic behavior in(311)AGaAs two-dimensional holes

We study two dimensional hole systems confined to GaAs quantum wells grown on the (311)A surface of GaAs substrates. Such samples exhibit an in-plane mobility anisotropy. At constant 2D hole density, we vary the symmetry of the quantum well potential and measure the temperature dependence of the resistivity along two different current directions, in a regime where the samples exhibit metallic behavior. The symmetry has a significant and non-trivial effect on the metallic behavior. Moreover, differences between the temperature-dependence of the resistivity along the two mobility directions point to specific scattering mechanisms being important in the expression of the metallic behavior.

Phase diagram of the integer quantum Hall effect inp-type germanium

We experimentally study the phase diagram of the integer quantized Hall effect, as a function of density and magnetic field. We used a two dimensional hole system confined in a Ge/SiGe quantum well, where all energy levels are resolved, because the Zeeman splitting is comparable to the cyclotron energy. At low fields and close to the quantum Hall liquid-to-insulator transition, we observe the floating up of the lowest energy level, but NO FLOATING of any higher levels, rather a merging of these levels into the insulating state. For a given filling factor, only direct transitions between the insulating phase and higher quantum Hall liquids are observed as a function of density. Finally, we observe a peak in the critical resistivity around filling factor one.

Hall measurements of the insulating phases at υ=1.5 and υ∼0.5 in p-type Si/Si 1−xGe x heterostructures using pulsed magnetic fields

Low temperature (0.3 K) Hall resistivities ( ρ xy ) of the two dimensional hole system in high quality p-type Si/Si 1−x Ge x single heterojunctions have been measured in pulsed magnetic fields to 50 T. Clean Hall measurements are obtained by subtracting the raw signals from four separate field pulses. Hall data are presented in the Landau level filling factor regime υ=1.5 where we have previously identified an insulating phase (IP). This IP, characterised by a rapid increase in ρ xx as T→0 K and non-linear I– V measurements, is shown to increase at large tilt angles. The corresponding Hall resistivity in the IP region, measured in tilted pulsed magnetic fields, remains finite and close to the classical value. Preliminary pulsed magneto-transport results are presented for a second IP which indicate that both ρ xx and ρ xy increase dramatically for υ<0.5.

Cyclotron resonance in p-type GaAs/GaAlAs single heterojunctions in pulsed high magnetic fields up to 40T

Far infrared cyclotron resonance experiments on a two dimensional hole system of GaAs/GaAlAs single heterojunction were performed in high pulsed magnetic fields. In the transmission spectra the cyclotron resonance was observed in the magnetic fields between 10 and 40T and laser photon energies between 3 and 10.5 meV. The temperature dependence of the resonance position and the magnetic field dependence of the linewidth are discussed under the consideration of the polaron screening effect and the filling factor in the 2-dimensional system.