On the Nature of Spin Currents

TL;DR

This paper derives explicit formulas for finite frequency spin and charge conductivities in Rashba and Luttinger systems, revealing distinct frequency behaviors and highlighting differences in their physical responses.

Contribution

It provides the first comprehensive expressions for spin and charge conductivities at finite frequencies in Rashba and Luttinger models, including generalized Rashba couplings.

Findings

Spin conductivity in Rashba systems matches dielectric polarizability frequency dependence.

Luttinger systems show different frequency dependence for spin and charge conductivities.

Generalized Rashba coupling leads to distinct frequency behaviors for spin and charge responses.

Abstract

Full expressions for finite frequency spin and charge conductivity in Rashba and Luttinger type systems are given. Whereas in the Rashba Hamiltonian the spin conductivity has the same frequency dependence as the dielectric polarizability, the Luttinger case is different. Moreover, for a generalized Rashba-type coupling the two quantities also exhibit different frequency dependencies.