Nonequilibrium dynamics of spontaneous symmetry breaking into a hidden state of charge-density wave

Abstract

Nonequilibrium phase transitions play a pivotal role in broad physical contexts, from condensed matter to cosmology. Tracking the formation of nonequilibrium phases in condensed matter requires a resolution of the long-range cooperativity on ultra-short timescales. Here, we study the spontaneous transformation of a charge-density wave in CeTe3 from a stripe order into a bi-directional state inaccessible thermodynamically but is induced by intense laser pulses. With ≈100 fs resolution coherent electron diffraction, we capture the entire course of this transformation and show self-organization that defines a nonthermal critical point, unveiling the nonequilibrium energy landscape. We discuss the generation of instabilities by a swift interaction quench that changes the system symmetry preference, and the phase ordering dynamics orchestrated over a nonadiabatic timescale to allow new order parameter fluctuations to gain long-range correlations. Remarkably, the subsequent thermalization locks the remnants of the transient order into longer-lived topological defects for more than 2 ns.

Toward nonthermal control of excited quantum materials: framework and investigations by ultrafast electron scattering and imaging

“…As the lattice potential changes leveled at the electronic scale is assumed to be nearly instantaneous, the soft modes in the critical regime (colored in red where the dispersion curves drop in frequency, ω) cannot respond adiabatically. This inherent nonadiabicity between the potential energy shift and the long-wave soft collective mode response is prominent for any photoinduced phase transition driven by a quench [23].…”

“…For example, within the high-critical temperature superconductors, such as iron-based and cuprates, superconductivity is often found to compete with a density-wave order. A prototypical case concerning the competitive SSB within the density-wave systems is recently discussed and observed in the rare-earth telluride compounds [22,23].…”

“…Nonetheless, we expect the post-quench immediate response to be potentialdriven. We first discuss here the truly competitive SSB scenario, applying to the rare-earth tritelluride system [23,72], in which T c is shared among the two order parameters η 1 and η 2 .…”

“…Meanwhile, the order parameter field of the present order, being driven directly by the quench, has a higher local temperature, i.e., T (2) T (1) in the initial period. Following this, it is possible for the new order parameter to undergo a threshold onset at a critical laser fluence F c , which is much smaller than what is required to completely melt the existing order [19,23]. However, if the system were to regain thermal equilibrium, i.e.…”

“…One can now rely on the growing capabilities of the ultrafast techniques to give increasingly more details of the nonequilibrium transformations between quantum phases; see for example the recent reviews [11][12][13][14]. Indeed, many recent ultrafast pump-probe studies of quantum matters also led to surprising results that cannot be identified from the equilibrium states [15][16][17][18][19][20][21][22][23], often referred to as the hidden state problem [24,25]. Second, studying the nonequilibrium collective state evolution in quantum materials involves fundamental concept of nonequilibrium many-body physics [26][27][28][29][30].…”