Spatial gradient of dynamic nuclear spin polarization induced by breakdown of quantum Hall effect

TL;DR

This study investigates how dynamic nuclear polarization (DNP) varies spatially in a quantum Hall effect breakdown regime, revealing a gradient along the electron drift direction through NMR signals measured at different probe positions.

Contribution

It demonstrates the spatial distribution of DNP in a Hall-bar device during QHE breakdown and shows that DNP develops along the electron drift direction, which was not previously characterized.

Findings

NMR signals vary with probe position in the Hall device.

Largest NMR signals are detected farthest from the electron-injecting electrode.

DNP develops along the electron drift direction during QHE breakdown.

Abstract

We studied spatial distribution of dynamic nuclear polarization (DNP) in a Hall-bar device in a breakdown regime of the quantum Hall effect (QHE). We detected nuclear magnetic resonance (NMR) signals from the polarized nuclear spins by measuring the Hall voltage $V_{xy}$ using three pairs of voltage probes attached to the conducting channel of the Hall bar. We find that the amplitude of the NMR signal depends on the position of the Hall voltage probes and that the largest NMR signal is obtained from the pair of probes farthest from the electron-injecting electrode. Combined with results on pump-and-probe measurements, we conclude that the DNP induced by QHE breakdown develops along the electron-drift direction.