Tracking Berry curvature effect in molecular dynamics by ultrafast magnetic x-ray scattering

TL;DR

This paper proposes a method to detect Berry curvature effects in molecular dynamics by using ultrafast magnetic x-ray scattering to observe spin density separation during photodissociation.

Contribution

It introduces a novel approach to probe Berry force effects through circular dichroism in ultrafast magnetic x-ray scattering, overcoming previous measurement challenges.

Findings

Berry force causes different dissociation rates for molecules with opposite spins.

Transient spin density separation can be reconstructed from x-ray scattering data.

The method enables direct observation of Berry curvature effects in molecular processes.

Abstract

The spin-dependent Berry force is a genuine effect of Berry curvature in molecular dynamics, which can dramatically result in spatial spin separation and change of reaction pathways. However, the way to probe the effect of Berry force remains challenging, because the time-reversal (TR) symmetry required for opposite Berry forces conflicts with TR symmetry breaking spin alignment needed to observe the effect, and the net effect could be transient for a molecular wave packet. We demonstrate that in molecular photodissociation, the dissociation rates can be different for molecules with opposite initial spin directions due to Berry force. We showcase that the spatially separated spin density, which is transiently induced by Berry force as the molecular wave packet passes through conical intersection, can be reconstructed from the circular dichroism (CD) of ultrafast non-resonant magnetic x-ray scattering using free electron lasers.