Hybrid superconductor–semiconductor heterostructures are a promising platform for quantum devices based on mesoscopic and topological superconductivity. In these structures, a semiconductor must be in close proximity to a superconductor and form an Ohmic contact. This can be accommodated in narrow bandgap semiconductors, such as InAs, where the surface Fermi level is positioned close to the conduction band. In this work, we study the structural properties of near-surface InAs quantum wells and find that surface morphology is closely connected to low-temperature transport, where electron mobility is highly sensitive to the growth temperature of the underlying graded buffer layer. By introducing an In0.81Al0.19As capping layer, we show that we change the surface Fermi level pinning of the In0.81Al0.19As thin film as compared to the In0.81Ga0.19As, giving rise to a tuning of the Fermi level in the InAs layer. Experimental measurements show a strong agreement with Schrödinger–Poisson calculations of the electron density, suggesting the conduction band energy of the In0.81Ga0.19As and In0.81Al0.19As surface is pinned to 40 and 309 meV above the Fermi level, respectively.

An effective Hamiltonian is derived to describe the conduction band of monolayer black phosphorus (phosphorene) in the presence of spin-orbit coupling and external electric field. Envelope function approximation along with symmetry arguments are utilized to derive extrinsic spin-orbit splitting, which is shown to be linear in both the magnitude of the external electric field and the strength of the atomic spin-orbit coupling. The spin splitting is akin to the Bychkov-Rashba expression but demonstrates an in-plane anisotropy. The spin relaxation of conduction electrons is then calculated within the Dyakonov-Perel mechanism where momentum scattering randomizes the polarization of a spin ensemble. We show how the anisotropic Fermi contour and the anisotropic extrinsic spin splitting contribute to the anisotropy of spin-relaxation time. Scattering centers in the substrate are considered to be charged impurities with screened Coulomb potential. We report that spin ensembles with different initial polarization in the plane of phosphorene show an anisotropy of more than an order of magnitude in spin-relaxation time.

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In this paper, we theoretically investigate plasmon propagation characteristics in AB and AA stacked bilayer graphene (BLG) in the presence of energy asymmetry due to an electrostatic field oriented perpendicularly to the plane of the graphene sheet. We first derive the optical conductivity of BLG using the Kubo formalism incorporating energy asymmetry and finite electron scattering. All results are obtained for room temperature (300K) operation. By solving Maxwell's equations in a dual gate device setup, we obtain the wavevector of propagating plasmon modes in the transverse electric (TE) and transverse magnetic (TM) directions at terahertz frequencies. The plasmon wavevector allows us to compare the compression factor, propagation length, and the mode confinement of TE and TM plasmon modes in bilayer and monolayer graphene sheets and also study the impact of material parameters on plasmon characteristics. Our results show that the energy asymmetry can be harnessed to increase the propagation length of TM plasmons in BLG. AA stacked BLG shows a larger increase in propagation length than AB stacked BLG; conversely, it is very insensitive to the Fermi level variations. Additionally, the dual gate structure allows independent modulation of the energy asymmetry and the Fermi level in BLG, which is advantageous for reconfiguring plasmon characteristics post device fabrication.

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In the presence of a 4π-periodic contribution to the current phase relation, for example in topological Josephson junctions, odd Shapiro steps are expected to be missing. While missing odd Shapiro steps have been observed in several material systems and interpreted in the context of topological superconductivity, they have also been observed in topologically trivial junctions. Here, we study the evolution of such trivial missing odd Shapiro steps in Al−InAs junctions in the presence of an in-plane magnetic field B θ . We find that the odd steps reappear at a crossover B θ value, exhibiting an in-plane field angle anisotropy that depends on spin−orbit coupling effects. We interpret this behavior by theoretically analyzing the Andreev bound state spectrum and the transitions induced by the nonadiabatic dynamics of the junction and attribute the observed anisotropy to mode-to-mode coupling. Our results highlight the complex phenomenology of missing Shapiro steps and the underlying current phase relations in planar Josephson junctions designed to realize Majorana states.

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