# Sub-picosecond photo-induced displacive phase transition in two-dimensional MoTe$_2$

## TL;DR

This study demonstrates a sub-picosecond, laser-induced phase transition in monolayer MoTe₂ from a semiconducting to a topological phase, driven by electronic excitations that soften lattice vibrations, enabling ultrafast control of topological properties.

## Contribution

First-principles calculations reveal a purely electronic, ultrafast phase transition mechanism in 2D MoTe₂ triggered by specific photon energies, advancing control over topological phases.

## Key findings

- Transition occurs within sub-picosecond timescale.
- Triggered by photons with energy over 1.96 eV.
- Carrier density needed is 3.4×10^{14} cm^{-2}.

## Abstract

Photo-induced phase transitions (PIPTs) provide an ultrafast, energy-efficient way for precisely manipulating the topological properties of transition-metal ditellurides, and can be used to stabilize a topological phase in an otherwise semiconducting material. Using first-principles calculations, we demonstrate that the PIPT in monolayer MoTe$_2$ from the semiconducting 2H phase to the topological 1T$'$ phase can be triggered purely by electronic excitations that soften multiple lattice vibrational modes. These softenings, driven by a Peierls-like mechanism within the conduction bands, lead to structural symmetry breaking within sub-picosecond timescales, which is shorter than the timescale of a thermally driven phase transition. The transition is predicted to be triggered by photons with energies over $1.96$\,eV, with an associated excited carrier density of $3.4\times10^{14}$\,cm$^{-2}$, which enables a controllable phase transformation by varying the laser wavelength. Our results provide insight into the underlying physics of the phase transition in 2D transition-metal ditellurides, and show an ultrafast phase transition mechanism for manipulation of the topological properties of 2D systems.