Photoinduced Enhancement of the Charge Density Wave Amplitude

TL;DR

This paper demonstrates that ultrafast photo-excitation can transiently enhance or induce large-amplitude charge density waves in elemental chromium through dynamic electron-phonon interactions, revealing a new way to control ordered states.

Contribution

It introduces a novel mechanism where ultrafast light pulses transiently enhance or induce charge density waves via electron-phonon coupling in chromium.

Findings

Photo-excitation can increase CDW amplitude by up to 30%.

Strong excitation induces a persistent, large-amplitude CDW state.

Dynamic electron-phonon interactions enable selective control of order parameters.

Abstract

Symmetry breaking and the emergence of order is one of the most fascinating phenomena in condensed matter physics. It leads to a plethora of intriguing ground states found in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting states of matter far from equilibrium can provide even more striking routes to symmetry-lowered, ordered states. Here, we demonstrate for the case of elemental chromium that moderate ultrafast photo-excitation can transiently enhance the charge-density-wave (CDW) amplitude by up to 30% above its equilibrium value, while strong excitations lead to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interactions, providing an efficient mechanism to selectively transform a broad excitation of the electronic order into a well defined, long-lived coherent lattice vibration. This mechanism may be exploited to transiently enhance order parameters in other systems with coupled degrees of freedom.