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

Abstract

The spinel-structure CuIr2S4 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.

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

“…This indicates that the symmetry-breaking lattice distortion is significantly affected only after the lattice degrees of freedom are heated close to T IM . This is consistent with the absorbed energy at F c that is comparable to the equilibrium enthalpy difference 45 between the high-T MC phase at T ∼ T IM and the low-T phase at T ∼ 100 K. Here the initial state T at t DP ∼ 5 µs (see Figure 6 (d)) is also estimated from the coherent mode frequencies.…”

“…The behavior is similar also at an increased F D = 8.1 mJ/cm 2 with slower recovery. 45 The suppression of the CO is delayed with respect to the D pulse for ∼ 0.6 ps (see inset to Figure 5) and does not depend on the small changes of the t DP delay 45 . The delay is consistent with the duration of the initial subpicosecond transient observed for the high-F transient reflectivity in Figure 3 (a).…”

“…The DWC phase emergence depends on the absorbed dose 35,44 , but the threshold dose was determined only for the case of high-energy ion irradiation 44 . Since the exact optical DWC-phase-creation conditions are not known we measured also the low-T DC photoconductivity (see Supplemental Material (SM) 45 ) and found, as suggested previously, 40 that even at the lowest feasible excitation fluences, F ∼100 µJ/cm 2 , the threshold dose is exceeded on a timescale faster than a single transient reflectivity scan acquisition time of ∼100 s. The pristine insulating triclinic phase is therefore inaccessible in the pump-probe experiments at low T and the previously reported 40 equilibrium low-T transient reflectivity refers to the DWC phase. Despite the absence of a long range Ir 4+ -dimer order in the DWC phase 37 the previously characterized coherent oscillations (CO) due to the displacive excitation of coherent phonons 40,45,46 (DECP) show well defined peaks with the low-T dephasing times exceeding ∼ 100 ps.…”

“…With increasing F P the CO appear suppressed in the F P -normalized scans and the signal becomes dominated by the sub-ps relaxation component. The detailed DECP-model 40,45 component analysis (see. Figure 4) reveals that the subps exponential component (SEC) amplitude, A e , departs from the low-F P linear dependence and starts to increase more steeply above F ce ∼ 0.6 mJ/cm 2 already (see inset to Figure 4 (e)).…”

Colloquium: Nonthermal pathways to ultrafast control in quantum materials

“…4(a), due to the formation of light-induced topological defects (Haupt et al, 2016; et al, 2017). Another example of an ultrafast transition induced by nonthermal electronic configurations is the switching into long-lived high-symmetry crystalline phases in prototypical Peierls systems, as shown by Huber et al, 2014;Naseska et al, 2021;and Teitelbaum et al, 2018 [Fig. 4(b)].…”