Structurally assisted melting of excitonic correlations in 1T-TiSe2

TL;DR

This study reveals that in 1T-TiSe2, structural destabilization, rather than electronic excitation alone, triggers the rapid melting of charge-density waves, highlighting a structurally assisted mechanism in ultrafast phase transitions.

Contribution

It demonstrates that structural disturbances can induce charge-density wave melting faster than electronic effects alone, challenging previous assumptions about ultrafast phase transition mechanisms.

Findings

Structural destabilization causes charge-density wave melting.

Melting occurs faster than electronic screening predicts.

Electron-phonon interactions enable different phase-transition pathways.

Abstract

The simultaneous condensation of electronic and structural degrees of freedom gives rise to new states of matter, including superconductivity and charge-density-wave formation. When exciting such a condensed system, it is commonly assumed that the ultrafast laser pulse disturbs primarily the electronic order, which in turn destabilizes the atomic structure. Contrary to this conception, we show here that structural destabilization of few atoms causes melting of the macroscopic ordered charge-density wave in 1T-TiSe2. Using ultrafast pump-probe non-resonant and resonant X-ray diffraction, we observe full suppression of the Se 4p orbital order and the atomic structure at excitation energies more than one order of magnitude below the suggested excitonic binding energy. Complete melting of the charge-density wave occurs 4-5 times faster than expected from a purely electronic charge-screening process, strongly suggesting a structurally assisted breakup of excitonic correlations. Our experimental data clarifies several questions on the intricate coupling between structural and electronic order in stabilizing the charge-density-wave in 1T-TiSe2. The results further show that electron-phonon-coupling can lead to different, energy dependent phase-transition pathways in condensed matter systems, opening new possibilities in the conception of non-equilibrium phenomena at the ultrafast scale.