First-order kinetics bottleneck during photoinduced ultrafast insulator–metal transition in 3D orbitally-driven Peierls insulator CuIr2S4

Abstract

The spinel-structure CuIr _2 S _4 compound displays a rather unusual orbitally-driven three-dimensional Peierls-like insulator–metal transition. The low- T symmetry-broken insulating state is especially interesting due to the existence of a metastable irradiation-induced disordered weakly conducting state. Here we study intense femtosecond optical pulse irradiation effects by means of the all-optical ultrafast multi-pulse time-resolved spectroscopy. We show that the structural coherence of the low- T broken symmetry state is strongly suppressed on a sub-picosecond timescale above a threshold excitation fluence resulting in a structurally inhomogeneous transient state which persists for several-tens of picoseconds before reverting to the low- T disordered weakly conducting state. The electronic order shows a transient gap filling at a significantly lower fluence threshold. The data suggest that the photoinduced-transition dynamics to the high- T metallic phase is governed by first-order-transition nucleation kinetics that prevents the complete ultrafast structural transition even when the absorbed energy significantly exceeds the equilibrium enthalpy difference to the high- T metallic phase.

Keywords

• ultrafast optical spectroscopy
• transient reflectivity
• coherent phonons
• CuIr2S4
• spinel
• ultrafast insulator–metal transition