Spin Berry phase in helical edge state: Transport signatures

Vivekananda Adak, Krishanu Roychowdhury, Sourin Das

Published 2019-05-07Version 1

Topological protection of edge state in quantum spin Hall systems relies only on time reversal symmetry, hence, S z conservation on the edge can be relaxed. This has consequence like spin Berry phase arising from a closed loop dynamics of the spin state of the electron. In distinction to most of the previous studies in this context, which have primarily been restricted to conserved S z , we investigate the effects of spin Berry phase induced by S z nonconservation on transport in a pristine edge. Our work provides a minimal framework to generate and detect these effects by employing spin-polarized leads in an interferometric set-up. Naively, one would expect that the measurements involving the edge state would be jeopardized due to the presence of spin polarized leads which can induce strong backscattering by destroying the time reversal symmetry at the tunnel-junctions. Quite contrary to the expectation, these leads turn out to be advantageous as they induce sharp Fano-type antiresonances with large visibility in the two-terminal conductance. As a function of energy (of the incident electron), the position of these antiresonances gets shifted owing to the presence of spin Berry phase, hence, serving as a smoking gun signal for S z nonconserving edge state.