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Register a new userEffective g factor of 2D holes in strained Ge quantum wells
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The effective g-factor of 2D holes in modulation doped mbox{p-SiGe/Ge/SiGe} structures was studied. The AC conductivity of samples with hole densities from $3.9 times 10^{11}$~to $6.2 times 10^{11}~text{cm}^{-2}$ was measured in perpendicular magnetic fields up to $8~text{T}$ using a contactless acoustic method. From the analysis of the temperature dependence of conductivity oscillations, the $mathrm{g}_{perp}$-factor of each sample was determined. The $mathrm{g}_{perp}$-factor was found to be decreasing approximately linearly with hole density. This effect is attributed to non-parabolicity of the valence band.
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Recently, lithographic quantum dots in strained-Ge/SiGe have become a promising candidate for quantum computation, with a remarkably quick progression from demonstration of a quantum dot to qubit logic demonstrations. Here we present a measurement of the out-of-plane $g$-factor for single-hole quantum dots in this material. As this is a single-hole measurement, this is the first experimental result that avoids the strong orbital effects present in the out-of-plane configuration. In addition to verifying the expected $g$-factor anisotropy between in-plane and out-of-plane magnetic ($B$)-fields, variations in the $g$-factor dependent on the occupation of the quantum dot are observed. These results are in good agreement with calculations of the $g$-factor using the heavy- and light-hole spaces of the Luttinger Hamiltonian, especially the first two holes, showing a strong spin-orbit coupling and suggesting dramatic $g$-factor tunability through both the $B$-field and the charge state.
We report measurements of the effective $g$ factor of low-density two-dimensional holes in a Ge quantum well. Using the temperature dependence of the Shubnikov-de Haas oscillations, we extract the effective $g$ factor in a magnetic field perpendicular to the sample surface. Very large values of the effective $g$ factor, ranging from $sim13$ to $sim28$, are observed in the density range of $1.4times10^{10}$ cm$^{-2}$ to $1.4times10^{11}$ cm$^{-2}$. When the magnetic field is oriented parallel to the sample surface, the effective $g$ factor is obtained from a protrusion in the magneto-resistance data that signifies full spin polarization. In the latter orientation, a small effective $g$ factor, $sim1.3-1.4$, is measured in the density range of $1.5times10^{10}$ cm$^{-2}$ to $2times10^{10}$ cm$^{-2}$. This very strong anisotropy is consistent with theoretical predictions and previous measurements in other 2D hole systems, such as InGaAs and GaSb.
We report density-dependent effective hole mass measurements in undoped germanium quantum wells. We are able to span a large range of densities ($2.0-11times10^{11}$ cm$^{-2}$) in top-gated field effect transistors by positioning the strained buried Ge channel at different depths of 12 and 44 nm from the surface. From the thermal damping of the amplitude of Shubnikov-de Haas oscillations, we measure a light mass of $0.061m_e$ at a density of $2.2times10^{11}$ cm$^{-2}$. We confirm the theoretically predicted dependence of increasing mass with density and by extrapolation we find an effective mass of $sim0.05m_e$ at zero density, the lightest effective mass for a planar platform that demonstrated spin qubits in quantum dots.
The results of experimental studies of the Shubnikov-de Haas (SdH) efect in the (013)-HgTe/Hg$_{1-x}$Cd$_x$Te quantum wells (QWs) of electron type of conductivity both with normal and inverted energy spectrum are reported. Comprehensive analysis of the SdH oscillations measured for the different orientations of magnetic field relative to the quantum well plane and crystallographic exes allows us to investigate the anisotropy of the Zeeman effect. For the QWs with inverted spectrum, it has been shown that the ratio of the spin splitting to the orbital one is strongly dependent not only on the orientation of the magnetic field relative to the QW plane but also on the orientation of the in-plane magnetic field component relative to crystallographic axes laying in the QW plane that implies the strong anisotropy of in-plane g-factor. In the QW with normal spectrum, this ratio strongly depends on the angle between the magnetic field and the normal to the QW plane and reveals a very slight anisotropy in the QW plane. To interpret the data, the Landau levels in the tilted magnetic field are calculated within the framework of four-band emph{kP} model. It is shown that the experimental results can be quantitatively described only with taking into account the interface inversion asymmetry.
We present angle-dependent measurements of the effective g-factor g* in a Ge-Si core-shell nanowire quantum dot. g* is found to be maximum when the magnetic field is pointing perpendicular to both the nanowire and the electric field induced by local gates. Alignment of the magnetic field with the electric field reduces g* significantly. g* is almost completely quenched when the magnetic field is aligned with the nanowire axis. These findings confirm recent calculations, where the obtained anisotropy is attributed to a Rashba-type spin-orbit interaction induced by heavy-hole light-hole mixing. In principle, this facilitates manipulation of spin-orbit qubits by means of a continuous high-frequency electric field.
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