Ultrafast spin density wave transition in Chromium governed by thermalized electron gas

TL;DR

This study demonstrates that the antiferromagnetic spin density wave in chromium can be completely destroyed within 100 femtoseconds using ultrafast photoexcitation, revealing that equilibrium phase transition concepts apply even in non-adiabatic regimes.

Contribution

It provides a quantitative analysis of the ultrafast SDW transition in chromium, linking the order parameter dynamics to the thermalized electron gas temperature.

Findings

SDW order parameter vanishes in under 100 fs

Ultrafast transition faster than charge density waves

Equilibrium phase transition concepts applicable in non-adiabatic regime

Abstract

The energy and momentum selectivity of time- and angle-resolved photoemission spectroscopy is exploited to address the ultrafast dynamics of the antiferromagnetic spin density wave (SDW) transition photoexcited in epitaxial thin films of chromium. We are able to quantitatively extract the evolution of the SDW order parameter $\Delta$ through the ultrafast phase transition. $\Delta$ is defined by the transient temperature of the thermalized electron gas. The complete destruction of SDW order on a sub-100~fs time scale is observed, much faster than for conventional charge density wave materials. Our results reveal that equilibrium concepts for phase transitions such as the order parameter may be utilized even in the strongly non-adiabatic regime of ultrafast photo-excitation.