Dynamic nuclear polarization induced by hot electrons

TL;DR

This paper introduces a novel local dynamic nuclear polarization technique in a GaAs/AlGaAs heterostructure, demonstrating how electron temperature influences nuclear spin polarization direction and relaxation rates at low temperatures.

Contribution

It presents a new method for local dynamic nuclear polarization using hot electrons in a heterostructure with variable channel width, revealing temperature-dependent polarization behavior.

Findings

Electron cooling causes nuclear polarization against the magnetic field.

Electron heating causes nuclear polarization toward the magnetic field.

Nuclear spin relaxation rate varies exponentially with inverse temperature.

Abstract

A new method for local dynamic nuclear polarization is demonstrated in a GaAs/AlGaAs heterostructure at the Landau level filling factor $\nu=3$. Using a narrow channel sample, where the width varies stepwise along the electron flow, we find that electron cooling (heating) causes the polarization of nuclear spins against (toward) the external magnetic field at liquid helium temperatures. The longitudinal nuclear spin relaxation rate varies exponentially with inverse temperature.