Quantum transport, anomalous dephasing, and spin-orbit coupling in an open ballistic bismuth nanocavity

The phase coherence time tau(phi) and spin-orbit coupling time tau(so) are measured in a bismuth quasiballistic nanocavity and in bismuth thin films using weak antilocalization and universal conductance fluctuations. The cavity is found to be zero dimensional for phase-coherent processes at low temperature. Weak antilocalization seems weakly affected by this drastic reduction of dimensionality. The temperature dependence of tau(phi) is similar in both types of samples, qualitatively consistent with low-energy transfer two-dimensional electron-electron interaction effects as the dominant dephasing mechanism. Strikingly, tau(phi) in the dot is found to be an order-of-magnitude smaller than in the film, and orders-of-magnitude smaller than the theoretical prediction.