Nuclear magnetic resonance probes for the Kondo scenario for the 0.7 feature in semiconductor quantum point contact devices

TL;DR

This paper proposes using nuclear magnetic resonance measurements, specifically nuclear relaxation and Knight shift, to test if the 0.7 conductance feature in quantum point contacts is caused by a bound electron, offering a new diagnostic tool.

Contribution

It introduces a novel nuclear magnetic resonance-based method to verify the presence of a bound electron as the origin of the 0.7 feature in quantum point contacts.

Findings

Bound electron presence increases nuclear relaxation rate

Temperature dependence of relaxation is non-monotonic

Nuclear relaxation combined with Knight shift can confirm the 0.7 feature origin

Abstract

We propose a probe based on nuclear relaxation and Knight shift measurements for the Kondo scenario for the "0.7 feature" in semiconductor quantum point contact (QPC) devices. We show that the presence of a bound electron in the QPC would lead to a much higher rate of nuclear relaxation compared to nuclear relaxation through exchange of spin with conduction electrons. Furthermore, we show that the temperature dependence of this nuclear relaxation is very non-monotonic as opposed to the linear-T relaxation from coupling with conduction electrons. We present a qualitative analysis for the additional relaxation due to nuclear spin diffusion (NSD) and study the extent to which NSD affects the range of validity of our method. The conclusion is that nuclear relaxation, in combination with Knight shift measurements, can be used to verify whether the 0.7 feature is indeed due to the presence of a bound electron in the QPC.