Ultrafast melting and recovery of collective order in the excitonic insulator Ta$_{2}$NiSe$_{5}$

TL;DR

This study uses ultrafast spectroscopy to explore the dynamics of the excitonic insulator Ta$_{2}$NiSe$_{5}$, revealing that electronic correlations are key to its order formation and demonstrating potential for ultrafast control of this phase.

Contribution

It provides new insights into the microscopic mechanisms behind excitonic order in Ta$_{2}$NiSe$_{5}$ using broadband ultrafast spectroscopy, highlighting the role of electronic correlations.

Findings

High-fluence photoexcitations suppress the excitonic order.

Electronic correlations are crucial for excitonic order formation.

Ultrafast quenching occurs within 50 femtoseconds.

Abstract

The layered chalcogenide Ta$_{2}$NiSe$_{5}$ has been proposed to host an excitonic condensate in its ground state, a phase that could offer a unique platform to study and manipulate many-body states at room temperature. However, identifying the dominant microscopic contribution to the observed spontaneous symmetry breaking remains challenging, perpetuating the debate over the ground state properties. Here, using broadband ultrafast spectroscopy we investigate the out-of-equilibrium dynamics of Ta$_{2}$NiSe$_{5}$ and demonstrate that the transient reflectivity in the near-infrared range is connected to the system's low-energy physics. We track the status of the ordered phase using this optical signature, establishing that high-fluence photoexcitations can suppress this order. From the sub-50 fs quenching timescale and the behaviour of the photoinduced coherent phonon modes, we conclude that electronic correlations provide a decisive contribution to the excitonic order formation. Our results pave the way towards the ultrafast control of an exciton condensate at room temperature.