Self-Polarization and Dynamical Cooling of Nuclear Spins in Double Quantum Dots

TL;DR

This paper predicts spontaneous nuclear polarization in double quantum dots, which can cool electrons below lattice temperature by creating a polarized nuclear spin environment, with specific conditions and time scales analyzed.

Contribution

It introduces the concept of self-polarization of nuclear spins in double quantum dots and explores its potential for dynamical cooling of electrons.

Findings

Nuclear polarization arises from an instability at resonance conditions.

Polarized nuclear spins can serve as a cold bath for electrons.

Conditions for observing self-polarization are discussed.

Abstract

Spontaneous nuclear polarization is predicted in double quantum dots in the spin-blocked electron transport regime. The polarization results from an instability of the zero-polarization state when singlet and triplet electron energy levels are brought into resonance by the effective hyperfine field of the nuclei on the electrons. The nuclear spins, once polarized, serve as a cold bath for cooling electrons below the lattice (phonon) temperature. We estimate the relevant time scales and discuss the conditions necessary to observe these phenomena.