Electrically-Driven Reverse Overhauser Pumping of Nuclear Spins in Quantum Dots

TL;DR

This paper introduces a novel electrically-driven method for nuclear spin polarization in quantum dots, enabling control over polarization direction and spatial modulation beyond traditional thermal bath mechanisms.

Contribution

It presents a new mechanism for nuclear spin polarization via electric modulation of hyperfine coupling, allowing for reverse Overhauser polarization and spatial control in quantum dots.

Findings

Polarization can be reversed relative to the Overhauser effect.

Electrical driving induces nuclear polarization through resonant excitation.

Spatial modulation of polarization occurs on sub-confinement scales.

Abstract

We propose a new mechanism for polarizing nuclear spins in quantum dots, based on periodic modulation of the hyperfine coupling by electric driving at the electron spin resonance frequency. Dynamical nuclear polarization results from resonant excitation rather than hyperfine relaxation mediated by a thermal bath, and thus is not subject to Overhauser-like detailed balance constraints. This allows polarization in the direction opposite to that expected from the Overhauser effect. Competition of the electrically-driven and bath assisted mechanisms can give rise to spatial modulation and sign reversal of polarization on a scale smaller than the electron confinement radius in the dot. The relation to reverse Overhauser polarization observed in GaAs quantum dots is discussed.