Probing the pathway of an ultrafast structural phase transition to illuminate the transition mechanism in Cu2S

TL;DR

This study uses ultrafast electron diffraction to investigate the structural phase transition in Cu2S nanocrystals, revealing that electron-phonon coupling primarily drives the transition, providing new insights into its mechanism.

Contribution

It demonstrates the ability to distinguish primary and secondary order parameters during a phase transition using ultrafast diffraction, highlighting electron-phonon coupling as the dominant mechanism.

Findings

Transient states along the transition pathway were observed.

The transition is primarily driven by electron-phonon interactions.

The study advances understanding of phase transition mechanisms in Cu2S.

Abstract

Disentangling the primary order parameter from secondary order parameters in phase transitions is critical to the interpretation of the transition mechanisms in strongly correlated systems and quantum materials. Here we present a study of structural phase transition pathways in superionic Cu2S nanocrystals that exhibit intriguing properties. Utilizing ultrafast electron diffraction techniques sensitive in both momentum-space and the time-domain, we distinguish the dynamics of crystal symmetry breaking and lattice expansion in this system. We are able to follow the transient states along the transition pathway and so observe the dynamics of both the primary and secondary order parameters. Based on these observations we argue that the mechanism of the structural phase transition in Cu2S is dominated by the electron-phonon coupling. This mechanism advances the understanding from previous results where the focus was solely on dynamic observations of the lattice expansion.