Reading charge transport from spin dynamics on the surface of topological insulator

TL;DR

This paper proposes a method to measure the charge transport properties of topological surface states by analyzing their spin dynamics using time-resolved spectroscopy, effectively isolating surface contributions from bulk effects.

Contribution

A non-perturbative diffusion equation is developed to connect spin dynamics with charge transport in topological insulators, enabling experimental detection of surface state properties.

Findings

Distinct Dyaknov-Perel spin relaxation behavior for TSSs and bulk

Spin decay time equals charge transport time in TSSs

Feasible femtosecond spectroscopy experiments proposed

Abstract

Resolving the conductance of the topological surface states (TSSs) from the bulk contribution has been a great challenge for studying the transport property of topological insulators. By developing a non-purturbative diffusion equation that describes fully the spin-charge dynamics in the strong spin-orbit coupling regime, we present a proposal to read the charge transport information of TSSs from its spin dynamics which can be isolated from the bulk contribution by time-resolved second harmonic generation pump-probe measurement. We demonstrate the qualitatively different Dyaknov-Perel spin relaxation behavior between the TSSs and the two-dimensional spin-orbit coupling electron gas. The decay time of both in-plane and out-of-plane spin polarization is naturally proved to be identical to the charge transport time. The out-of-plane spin dynamics is shown to be in the experimentally reachable regime of the femtosecond pump probe spectroscopy and thereby we suggest experiments to detect the charge transport property of the TSSs from their unique spin dynamics.