Quantum many-body dynamics of the Einstein-de Haas effect

TL;DR

This paper introduces a quantum many-body theory using angulon quasiparticles to model the Einstein-de Haas effect, revealing femtosecond timescale angular momentum transfer even with weak coupling.

Contribution

It presents a novel rotationally invariant quantum many-body approach to model electron-lattice angular momentum transfer using angulon quasiparticles.

Findings

Non-perturbative effects occur at weak coupling

Angular momentum transfer happens on femtosecond timescales

The theory advances understanding of ultrafast magnetism

Abstract

In 1915, Einstein and de Haas and Barnett demonstrated that changing the magnetization of a magnetic material results in mechanical rotation, and vice versa. At the microscopic level, this effect governs the transfer between electron spin and orbital angular momentum, and lattice degrees of freedom, understanding which is key for molecular magnets, nano-magneto-mechanics, spintronics, and ultrafast magnetism. Until now, the timescales of electron-to-lattice angular momentum transfer remain unclear, since modeling this process on a microscopic level requires addition of an infinite amount of quantum angular momenta. We show that this problem can be solved by reformulating it in terms of the recently discovered angulon quasiparticles, which results in a rotationally invariant quantum many-body theory. In particular, we demonstrate that non-perturbative effects take place even if the electron--phonon coupling is weak and give rise to angular momentum transfer on femtosecond timescales.