Mode-selective ballistic pathway to a metastable electronic phase

TL;DR

This study demonstrates how selective vibrational excitation can control the metal-insulator transition in indium wires, revealing the ballistic nature of the structural change and enabling dynamic material property manipulation.

Contribution

It provides the first experimental evidence of mode-selective control over a phase transition using tailored ultrafast pulses and confirms the ballistic transition pathway through ab initio simulations.

Findings

Selective excitation of phonon modes controls the phase transition.

The transition follows a ballistic pathway along Peierls modes.

Coherent exciton-phonon interactions enable dynamic control.

Abstract

Exploiting vibrational excitation for the dynamic control of material properties is an attractive goal with wide-ranging technological potential. Most metal-to-insulator transitions are mediated by few structural modes and are thus ideal candidates for the selective driving towards a desired electronic phase. Such targeted navigation within a generally multi-dimensional potential energy landscape requires microscopic insight into the non equilibrium pathway. However, the exact role of coherent inertial motion across the transition state has remained elusive. Here, we demonstrate mode-selective control over the metal-to-insulator phase transition of atomic indium wires on the Si(111) surface, monitored by ultrafast low-energy electron diffraction. We use tailored pulse sequences to individually enhance or suppress key phonon modes and thereby steer the collective atomic motion within the potential energy surface underlying the structural transformation. Ab initio molecular dynamics simulations demonstrate the ballistic character of the structural transition along the deformation vectors of the Peierls amplitude modes. Our work illustrates that coherent excitation of collective modes via exciton-phonon interactions evades entropic barriers and enables the dynamic control of materials functionality.