R. L. Kallaher

Spin-orbit interaction and spin coherence in narrow-gap semiconductor and semimetal wires

Spin-dependent quantum transport experiments on InSb and InAs heterostructures and Bi thin films are discussed, focusing on mesoscopic geometries where spin-orbit interaction and quantum coherence determine the properties. The narrow-bandgap semiconductors InSb and InAs, and the semimetal Bi have substantial spin-orbit interaction. The experiments use antilocalization to study spin-orbit interaction and spin coherence lengths in nanolithographic wires fabricated on the materials. In the three systems the spin coherence lengths increase with decreasing wire widths if other parameters stay constant, of technological importance for spin-based devices. The experiments also indicate that Bi has surface states with Rashba-like spin-orbit interaction. A quasi-one-dimensional model of antilocalization, as fitted to the data, is explained and its consequences for quantum coherence in mesoscopic structures is explored. A united understanding of the experiments is presented relying on the duality between the Aharonov-Bohm and the Aharonov-Casher phases, the latter resulting from spin-orbit interaction. The duality strengthens the analogy between phenomena under magnetic fields and under spin-orbit interaction.

Dependence of the Spin Coherence Length on Wire Width for Quasi‐1‐Dimensional InSb and InAs Wires and Bi Wire Surface States

In diffusive two‐dimensional electron systems (2DESs) with linear spin‐orbit interaction (SOI), quasi‐one‐dimensional (Q1D) confinement in narrow wires of width W is theoretically predicted to result in an enhancement of the spin relaxation length LS, such that LS∝1/W. We present our experimental data of the dependence of LS on W for three different systems: 1) ballistic InSb wires with specular boundary scattering and strong Dresselhaus SOI, 2) ballistic InAs wires with diffusive boundary scattering and Rashba SOI, and 3) diffusive bismuth wires with a large density of states at the surface. For all three systems, information on the spin relaxation is gathered from the weak‐antilocalization effect (WAL), a magnetotransport measurement sensitive to both the spin‐orbit coherence length and the phase coherence length Lφ. We find a dependence of LS on W, where LS increases with decreasing W in all three systems. However, the theory is valid for Q1D diffusive wires with linear SOI, which does not fit the prof...

Magnetoelectric Mapping as Observed in Quantum Coherence Phenomena under Strong Spin-Orbit Interaction

A magnetoelectric mapping is demonstrated between dephasing effects of the magnetic vector potential and effects of an effective vector potential describing spin-orbit interaction. The experiments use spin-dependent mesoscopic quantum transport experiments on the narrow-gap semiconductor InSb and the semimetal Bi, both materials with strong spin-orbit interaction. The spin-orbit-induced antilocalization signature in transport allows determination of spin coherence lengths in narrow InSb and Bi wires. Spin coherence lengths are observed to increase with decreasing wire widths. The geometrical effect of width can be understood from the magnetoelectric duality between the Aharonov-Bohm phase and the Aharonov-Casher phase.