Role of chiral quantum Hall edge states in nuclear spin polarization

TL;DR

This paper reveals how chiral edge states in quantum Hall ferromagnets influence nuclear spin polarization, enhancing understanding of RDNMR responses and enabling more robust quantum measurements.

Contribution

It uncovers the role of chiral edge modes in dynamic nuclear polarization within quantum Hall ferromagnets, a previously unrecognized effect.

Findings

Chiral edge states significantly affect nuclear spin polarization.

Unidirectional edge currents make polarization robust at high temperatures.

Reciprocity in RDNMR response observed due to edge state effects.

Abstract

Resistively detected NMR (RDNMR) based on dynamic nuclear polarization (DNP) in a quantum Hall ferromagnet (QHF) is a highly-sensitive method for the discovery of fascinating quantum Hall phases; however, the mechanism of this DNP and in particular the role of quantum Hall edge states in it are unclear. Here we demonstrate the important but previously unrecognized effect of chiral edge modes on the nuclear spin polarization. A side-by-side comparison of the RDNMR signals from Hall bar and Corbino disk configurations allows us to distinguish the contributions of bulk and edge states to DNP in QHF. The unidirectional current flow along chiral edge states makes the polarization robust to thermal fluctuations at high temperatures and makes it possible to observe a reciprocity principle of the RDNMR response. These findings help us better understand complex NMR responses in QHF, which has important implications for the development of RDNMR techniques.