We have studied quantum-well-confined holes based on the Luttinger-model description for the valence band of typical semiconductor materials. Even when only the lowest quasi-two-dimensional (quasi-2D) subband is populated, the static spin susceptibil
ity turns out to be very different from the universal isotropic Lindhard-function lineshape obtained for 2D conduction-electron systems. The strongly anisotropic and peculiarly density-dependent spin-related response of 2D holes at long wavelengths should make it possible to switch between easy-axis and easy-plane magnetization in dilute magnetic quantum wells. An effective g factor for 2D hole systems is proposed.
Refraction, interference, and diffraction serve as distinguishing features for wave-like phenomena. While they are normally associated only with a purely spatial wave-propagation pattern, analogs to interference and diffraction involving the spatio-t
emporal dynamics of waves in one dimension (1D) have been pointed out. Here we complete the triplet of analogies by discussing how spatio-temporal analogs to refraction are exhibited by a quantum particle in 1D that is scattering off a step barrier. Similarly, birefringence in spacetime occurs for a spin-1/2 particle in a magnetic field. These examples serve to illustrate basics of quantum time evolution from a new perspective.
We have performed a theoretical study of electronic transport in single and bilayer graphene based on the standard linear-response (Kubo) formalism and continuum-model descriptions of the graphene band structure. We are focusing especially on the int
erband contribution to the optical conductivity. Analytical results are obtained for a variety of situations, which allow clear identification of features in the conductivity that are associated with relevant electronic energy scales. Our work extends previous numerical studies and elucidates ways to infer electronic properties of graphene samples from optical-conductivity measurements.
We have calculated the optical conductivity of a disorder-free single graphene sheet in the presence of spin-orbit coupling, using the Kubo formalism. Both intrinsic and structural-inversion-asymmetry induced types of spin splitting are considered wi
thin a low-energy continuum theory. Analytical results are obtained that allow us to identify distinct features arising from spin-orbit couplings. We point out how optical-conductivity measurements could offer a way to determine the strengths of spin splitting due to various origins in graphene.
We have obtained numerically exact results for the spin-related geometric quantum phases that arise in p-type semiconductor ring structures. The interplay between gate-controllable (Rashba) spin splitting and quantum-confinement-induced mixing betwee
n hole-spin states causes a much higher sensitivity of magnetoconductance oscillations to external parameters than previously expected. Our results imply a much-enhanced functionality of hole-ring spin-interference devices and shed new light on recent experimental findings.
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 su
bbands. We elucidate the interplay between quantum confinement and heavy-hole - light-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.
We present a theoretical study of spin-3/2 hole transport through mesoscopic rings, based on the spherical Luttinger model. The quasi-one-dimensional ring is created in a symmetric two-dimensional quantum well by a singular-oscillator potential for t
he radial in-plane coordinate. The quantum-interference contribution to the two-terminal ring conductance exhibits an energy-dependent Aharonov-Anandan phase, even though Rashba and Dresselhaus spin splittings are absent. Instead, confinement-induced heavy-hole - light-hole mixing is found to be the origin of this phase, which has ramifications for magneto-transport measurements in gated hole rings.
