Nonequilibrium Charge-Density-Wave Order Beyond the Thermal Limit

TL;DR

This paper demonstrates the existence of nonthermal charge-density-wave order at electronic temperatures exceeding the thermodynamic transition point, revealing new nonequilibrium phenomena in strongly excited systems.

Contribution

It provides experimental evidence and theoretical modeling of nonthermal CDW order beyond the thermal limit using advanced spectroscopic techniques.

Findings

Nonthermal CDW order persists at high electronic temperatures.

Distinct dynamics of CDW recovery compared to equilibrium.

Time-dependent Ginzburg-Landau model explains the observed phenomena.

Abstract

The interaction of many-body systems with intense light pulses may lead to novel emergent phenomena far from equilibrium. Recent discoveries, such as the optical enhancement of the critical temperature in certain superconductors and the photo-stabilization of hidden phases, have turned this field into an important research frontier. Here, we demonstrate nonthermal charge-density-wave (CDW) order at electronic temperatures far greater than the thermodynamic transition temperature. Using time- and angle-resolved photoemission spectroscopy and time-resolved X-ray diffraction, we investigate the electronic and structural order parameters of an ultrafast photoinduced CDW-to-metal transition. Tracking the dynamical CDW recovery as a function of electronic temperature reveals a behaviour markedly different from equilibrium, which we attribute to the suppression of lattice fluctuations in the transient nonthermal phonon distribution. A complete description of the system's coherent and incoherent order-parameter dynamics is given by a time-dependent Ginzburg-Landau framework, providing access to the transient potential energy surfaces.