Multi-mode excitation drives disorder during the ultrafast melting of a C4-symmetry-broken phase

TL;DR

This study reveals that ultrafast light excitation causes inhomogeneous disordering in a layered manganite, challenging existing mean-field theories and highlighting the importance of disorder in photoinduced phase transitions.

Contribution

The paper demonstrates that disorder plays a crucial role in ultrafast phase transitions, showing limitations of mean-field models in describing light-induced symmetry restoration.

Findings

Ultrafast inhomogeneous disordering occurs in La0.5Sr1.5MnO4.

Mean-field order parameters do not reflect atomic-scale states during transition.

Disorder may be a common feature in light-induced phase changes.

Abstract

Spontaneous C4-symmetry breaking phases are ubiquitous in layered quantum materials, and often compete with other phases such as superconductivity. Preferential suppression of the symmetry broken phases by light has been used to explain non-equilibrium light induced superconductivity, metallicity, and the creation of metastable states. Key to understanding how these phases emerge is understanding how C4 symmetry is restored. A leading approach is based on time-dependent Ginzburg-Landau theory, which explains the coherence response seen in many systems. However, we show that, for the case of the single layered manganite La0.5Sr1.5MnO4, the theory fails. Instead, we find an ultrafast inhomogeneous disordering transition in which the mean-field order parameter no longer reflects the atomic-scale state of the system. Our results suggest that disorder may be common to light-induced phase transitions, and methods beyond the mean-field are necessary for understanding and manipulating photoinduced phases.