Bypassing the structural bottleneck in the ultrafast melting of electronic order

TL;DR

This study demonstrates that ultrafast vibrational disordering caused by hot-electron energy dissipation can rapidly quench the electronic spectral gap in a charge-density-wave material within 60 fs, bypassing the structural bottleneck.

Contribution

It provides direct experimental evidence that incoherent lattice motion plays a crucial role in ultrafast electronic order melting, challenging previous assumptions about the timescale of lattice influence.

Findings

Spectral gap collapses in about 60 fs due to vibrational disordering.

Lattice vibrations influence electronic order faster than the structural oscillation timescale.

Incoherent lattice motion is key in photo-induced electronic order quenching.

Abstract

The emergent properties of quantum materials, such as symmetry-broken phases and associated spectral gaps, can be effectively manipulated by ultrashort photon pulses. Impulsive optical excitation generally results in a complex non-equilibrium electron and lattice dynamics that involves multiple processes on distinct timescales, and a common conception is that for times shorter than about 100 fs the gap in the electronic spectrum is not seriously affected by lattice vibrations. Here, we directly monitor the photo-induced collapse of the spectral gap in a canonical charge-density-wave material, blue bronze Rb0.3MoO3. We find that ultra-fast (about 60 fs) vibrational disordering due to efficient hot-electron energy dissipation quenches the gap significantly faster than the typical structural bottleneck time corresponding to one half-cycle oscillation (about 315 fs) of the coherent charge-density-wave amplitude mode. This result not only demonstrates the importance of incoherent lattice motion in the photo-induced quenching of electronic order, but also resolves the perennial debate about the nature of the spectral gap in a coupled electron-lattice system.