Nuclear spin dynamics in the quantum regime of a single-molecule magnet

TL;DR

This study reveals that nuclear spin dynamics in a single-molecule magnet at very low temperatures are driven by quantum tunneling and spin diffusion, with nuclear spins remaining thermally coupled to phonons even in the quantum regime.

Contribution

It provides the first experimental evidence of nuclear spins maintaining thermal contact with phonons deep in the quantum regime and introduces a simple model for tunneling-induced nuclear relaxation.

Findings

Nuclear spin dynamics are governed by quantum tunneling and spin diffusion.

Nuclear spins stay in thermal contact with phonons even at sub-Kelvin temperatures.

A simple model explains how tunneling fluctuations relax nuclear polarization.

Abstract

We show that the nuclear spin dynamics in the single-molecule magnet Mn12-ac below 1 K is governed by quantum tunneling fluctuations of the cluster spins, combined with intercluster nuclear spin diffusion. We also obtain the first experimental proof that - surprisingly - even deep in the quantum regime the nuclear spins remain in good thermal contact with the lattice phonons. We propose a simple model for how T-independent tunneling fluctuations can relax the nuclear polarization to the lattice, that may serve as a framework for more sophisticated theories.