Cooling and heating nuclear spins by strongly localized electrons

TL;DR

This paper develops a microscopic theory for nuclear spin thermodynamics in systems with strongly localized electrons, revealing conditions for efficient nuclear spin cooling and how magnetic fields influence spin dynamics.

Contribution

It introduces a new microscopic model bridging existing theories, describing nuclear spin behavior with long electron spin correlation times in quantum dots.

Findings

Efficient nuclear spin cooling requires strong external magnetic fields.

Nuclear spin heating times vary significantly with magnetic field strength.

The theory explains deviations from traditional spin temperature concepts in localized electron systems.

Abstract

The concept of nuclear spin temperature has been a cornerstone of the theory of dynamic nuclear spin polarization by electrons in various semiconductor structures for decades. Still, it is not always applicable to strongly localized electrons due to their long spin correlation times. This motivated the use of the oversimplified central spin model for the description of the nuclear spin dynamics in quantum dots. Here, we present a microscopic theory that bridges the gap between these two approaches by describing the nuclear spin thermodynamics for systems with long electron spin correlation times. Importantly, our theory predicts that efficient nuclear spin cooling by strongly localized electrons requires an external magnetic field by far exceeding the local field of nuclear spin-spin interaction, and that the time of the nuclear spin heating by unpolarized electrons may change by several orders of magnitude depending on the magnetic field.