Non-universal conductance in quasi-helical quantum wires

TL;DR

This paper demonstrates that in quasi-helical quantum wires, conductance is non-universal and depends on interactions, contrasting with ideal helical systems where conductance is quantized, due to spin-charge mixing effects.

Contribution

It reveals that partially gapped quasi-helical wires exhibit non-universal conductance influenced by interactions, challenging the assumption of quantized conductance in such systems.

Findings

Conductance in quasi-helical wires is non-universal and interaction-dependent.

Spin-charge mixing leads to a non-helical low-energy Hamiltonian.

Universal conductance quantization does not hold in these systems.

Abstract

In a quantum wire with ideal helical modes, the conductance is quantized in units of e^2/h, provided the wire is connected to Fermi liquid leads. We show that this universality does not hold in partially gapped quasi-helical systems such as Rashba nanowires subject to a magnetic field, which are commonly used to mimic helical Luttinger liquids. Instead, their conductance takes a non-universal value that depends on the interactions in the wire, even in the presence of Fermi liquid leads. The non-universal conductance is rooted in a non-trivial mixing of spin and charge degrees of freedom, which in turn defines a non-helical low-energy Hamiltonian.