Helical nuclear spin order in two-subband quantum wires

TL;DR

This paper investigates how nuclear spins in two-subband quantum wires form a helical order due to hyperfine interactions, leading to conductance reduction and complex spin patterns at low temperatures.

Contribution

It introduces the concept of a superposition of two helical nuclear spin orders in two-subband quantum wires and analyzes their impact on electronic properties.

Findings

Nuclear spins form a superposition of two helices with distinct pitches.

The nuclear spin order causes a two-step reduction in conductance.

The mechanism involves an interaction-enhanced RKKY exchange leading to partial electron spectrum gapping.

Abstract

In quantum wires, the hyperfine coupling between conduction electrons and nuclear spins can lead to a (partial) ordering of both of them at low temperatures. By an interaction-enhanced mechanism, the nuclear spin order, caused by RKKY exchange, acts back onto the electrons and gaps out part of their spectrum. In wires with two subbands characterized by distinct Fermi momenta kF1 and kF2, the nuclear spins form a superposition of two helices with pitches {\pi}/kF1 and {\pi}/kF2, thus exhibiting a beating pattern. This order results in a reduction of the electronic conductance in two steps upon lowering the temperature.