Self-sustaining dynamical nuclear polarization oscillations in quantum dots

TL;DR

This paper presents a minimal model explaining large, self-sustained nuclear polarization oscillations in quantum dots, driven by spin-dependent tunneling and nuclear spin diffusion, matching experimental observations of long periods.

Contribution

It introduces a realistic coupled electron-nuclear spin dynamics model that explains the origin of robust oscillations in quantum dot systems.

Findings

Explains long oscillation periods up to hundreds of seconds.

Accounts for differences between vertical and lateral quantum dot structures.

Supports the hypothesis that nuclear-spin-dependent tunneling causes oscillations.

Abstract

Early experiments on spin-blockaded double quantum dots revealed surprising robust, large-amplitude current oscillations in the presence of a static (dc) source-drain bias [see e.g. K. Ono, S. Tarucha, Phys. Rev. Lett. 92, 256803 (2004)]. Experimental evidence strongly indicates that dynamical nuclear polarization plays a central role, but the mechanism has remained a mystery. Here we introduce a minimal albeit realistic model of coupled electron and nuclear spin dynamics which supports robust self-sustained oscillations. Our mechanism relies on a nuclear-spin analog of the tunneling magnetoresistance phenomenon (spin-dependent tunneling rates in the presence of an inhomogeneous Overhauser field) and nuclear spin diffusion, which governs dynamics of the spatial profile of nuclear polarization. The extremely long oscillation periods (up to hundreds of seconds) observed in experiments as well as the differences in phenomenology between vertical and lateral quantum dot structures are naturally explained in the proposed framework.