The theory of coherent dynamic nuclear polarization in quantum dots

TL;DR

This paper develops a semi-classical theory of dynamic nuclear polarization in quantum dots, identifying geometrical and dynamic contributions and explaining experimental oscillations through detailed numerical analysis.

Contribution

It introduces a semi-classical framework distinguishing geometrical and dynamic polarization contributions in DNP, with analysis of control parameter effects and explanation of observed oscillations.

Findings

DNP has geometrical and dynamic components with different parameter dependencies.

Dynamic polarization dominates with long waiting times near the S-T+ crossing.

Numerical analysis explains experimental oscillations observed by Foletti et al.

Abstract

We consider the dynamic nuclear spin polarization (DNP) using two electrons in a double quantum dot in presence of external magnetic field and spin-orbit interaction, in various schemes of periodically repeated sweeps through the S-T+ avoided crossing. By treating the problem semi-classically, we find that generally the DNP have two distinct contributions - a geometrical polarization and a dynamic polarization, which have different dependence on the control parameters such as the sweep rates and waiting times in each period. Both terms show non-trivial dependence on those control parameter. We find that even for small spin-orbit term, the dynamical polarization dominates the DNP in presence of a long waiting period near the S-T+ avoided crossing, of the order of the nuclear Larmor precession periods. A detailed numerical analysis of a specific control regime can explain the oscillations observed by Foletti et.~al.~in arXiv:0801.3613.