First-order kinetics bottleneck during photoinduced ultrafast insulator-metal transition in 3D orbitally-driven Peierls insulator CuIr$_{2}$S$_{4}$

TL;DR

This study investigates the ultrafast photoinduced insulator-metal transition in CuIr₂S₄, revealing that structural changes follow first-order kinetics while electronic order is transiently suppressed independently, highlighting complex transition dynamics.

Contribution

It demonstrates that structural transition dynamics are governed by first-order nucleation kinetics, distinct from the electronic transition, in a 3D orbitally-driven Peierls insulator.

Findings

Structural coherence is suppressed within sub-picoseconds above a threshold fluence.

Transient electronic gap filling occurs at a lower fluence threshold.

Structural transition is hindered by first-order nucleation kinetics despite high energy input.

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. In contrast, the dynamically-decoupled electronic order is transiently suppressed on a sub-picosecond timescale rather independently due to a photoinduced Mott transition.