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.