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Register a new userStrong Transport Anisotropy in a Ge/SiGe Quantum Well in Tilted Magnetic Fields
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We report on a strong transport anisotropy in a 2D hole gas in a Ge/SiGe quantum well, which emerges only when both perpendicular and in-plane magnetic fields are present. The ratio of resistances, measured along and perpendicular to the in-plane field, can exceed $3times 10^4$. The anisotropy occurs in a wide range of filling factors where it is determined {em primarily} by the tilt angle. The lack of significant anisotropy without an in-plane field, easy tunability, and persistence to higher temperatures and filling factors set this anisotropy apart from nematic phases in GaAs/AlGaAs.
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Recent study of a high-mobility 2D hole gas in a strained Ge quantum well revealed strong transport anisotropy in the quantum Hall regime when the magnetic field was tilted away from the sample normal. In the present study we demonstrate that the anisotropy persists to such high temperatures and filling factors that quantum oscillations are no longer observed. This finding rules out the formation of a stripe phase as a possible origin for the observed anisotropy. However, we also show that the observed anisotropy is not consistent with other known anisotropies, such as those arising from finite thickness effects or surface roughness.
We investigate the double-layer electron system in a parabolic quantum well at filling factor $ u=2$ in a tilted magnetic field using capacitance spectroscopy. The competition between two ground states is found at the Zeeman splitting appreciably smaller than the symmetric-antisymmetric splitting. Although at the transition point the system breaks up into domains of the two competing states, the activation energy turns out to be finite, signaling the occurrence of a new insulator-insulator quantum phase transition. We interpret the obtained results in terms of a predicted canted antiferromagnetic phase.
We report the observation of an electron gas in a SiGe/Si/SiGe quantum well with maximum mobility up to 240 m^2/Vs, which is noticeably higher than previously reported results in silicon-based structures. Using SiO, rather than Al_2O_3, as an insulator, we obtain strongly reduced threshold voltages close to zero. In addition to the predominantly small-angle scattering well known in the high-mobility heterostructures, the observed linear temperature dependence of the conductivity reveals the presence of a short-range random potential.
We have determined the Lande factor g* in self-organized InAs quantum dots using resonant-tunnelling experiments. With the magnetic field applied parallel to the growth direction z we find g*_parallel = 0.75 for the specific dot investigated. When the magnetic field is tilted away by theta from the growth axis, g* gradually increases up to a value g*_perp = 0.92 when B perp z. Its angular dependence is found to follow the phenomenological behaviour g* (theta) = sqrt{(g*_parallel cos(theta)^2 + (g*_perp sin(theta)^2}.
We report the results of an experimental study of the magnetoresistance $rho_{xx}$ in two samples of $p$-Si/SiGe/Si with low carrier concentrations $p$=8.2$times10^{10}$ cm$^{-2}$ and $p$=2$times10^{11}$ cm$^{-2}$. The research was performed in the temperature range of 0.3-2 K in the magnetic fields of up to 18 T, parallel to the two-dimensional (2D) channel plane at two orientations of the in-plane magnetic field $B_{parallel}$ against the current $I$: $B_{parallel} perp I$ and $B_{parallel} parallel I$. In the sample with the lowest density in the magnetic field range of 0-7.2 T the temperature dependence of $rho_{xx}$ demonstrates the metallic characteristics ($d rho_{xx}/dT>$0). However, at $B_{parallel}$ =7.2 T the derivative $d rho_{xx}/dT$ reverses the sign. Moreover, the resistance depends on the current orientation with respect to the in-plane magnetic field. At $B_{parallel} cong$ 13 T there is a transition from the dependence $ln(Deltarho_{xx} / rho_{0})propto B_{parallel}^2$ to the dependence $ln(Deltarho_{xx} / rho_{0})propto B_{parallel}$. The observed effects can be explained by the influence of the in-plane magnetic field on the orbital motion of the charge carriers in the quasi-2D system.
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