Photoinduced multistage phase transitions in Ta2NiSe5

TL;DR

This study demonstrates ultrafast, multistage photoinduced phase transitions in Ta2NiSe5, including a long-lived insulator-to-metal transition with structural changes, achieved through controlled photoexcitation.

Contribution

It introduces a combined approach of transport, ultrafast spectroscopy, and microscopy to observe and control multistage phase transitions in Ta2NiSe5.

Findings

Photoinduced resistivity drops by over four orders of magnitude.

A thermally stable, structurally distinct metallic state is achieved.

Nano-sheet samples are essential for complete phase transition.

Abstract

Utrafast control of material physical properties represents a rapid developing field in condensed matter physics. Yet, accessing to the long-lived photoinduced electronic states is still in its early stage, especially with respect to an insulator to metal phase transition. Here, by combing transport measurement with ultrashort photoexcitation and coherent phonon spectroscopy, we report on photoinduced multistage phase transitions in Ta2NiSe5. Upon excitation by weak pulse intensity, the system is triggered to a short-lived state accompanied by a structural change. Further increasing the excitation intensity beyond a threshold, a photoinduced steady new state is achieved where the resistivity drops by more than four orders at temperature 50 K. This new state is thermally stable up to at least 350 K and exhibits the lattice structure different from any of the thermally accessible equilibrium states. Transmission electron microscopy reveals an in-chain Ta atom displacement in the photoinduced new structure phase. We also found that nano-sheet samples with the thickness less than the optical penetration depth are required for attaining a complete transition.