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

Spontaneous C-4-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 C-4 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. Light-induced phase transitions are typically described by a time-dependent mean-field theory. Here, the authors show that such a theory fails to capture the order parameter dynamics in a single layered manganite and discuss the role of disorder in ultrafast phase transitions in general.

Automated summary

Spontaneous C-4-symmetry breaking phases are common in layered quantum materials and compete with other phases. However, traditional theories fail to explain certain materials, indicating the need for methods beyond mean-field to understand light-induced phase transitions.