Sub-picosecond photo-induced displacive phase transition in two-dimensional MoTe2

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 MoTe2 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 × 1014 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.

Microscopic force driving the photoinduced ultrafast phase transition: Time-dependent density functional theory simulations of IrTe2

“…This failure to have the LT-to-HT phase transition at stronger laser intensity is rather striking. Such nonmonotonic laser-intensity dependence of the dynamic process is highly unexpected in terms of previously proposed mechanisms [28] for photoinduced phase transitions.…”

Terahertz Driven Reversible Topological Phase Transition of Monolayer Transition Metal Dichalcogenides

“…Actually, the optical absorption could also change the energy landscape and trigger phase transition. [ 10 ] When the defect or impurity concentration is not high enough, we can phenomenologically incorporate its effect by adopting finite lifetime in the response formulae, Equations () and (). The current theoretical work is based on the perfect crystal, and a complete evaluation on defects and impurities is out of scope here.…”

Topological phonons in oxide perovskites controlled by light

“…Photoexcited carriers are simulated by promoting electrons from high-energy valence band states to low-energy conduction band states. This Δ self-consistent field (ΔSCF) method introduces noninteracting electron-hole pairs by changing the occupation numbers of the Kohn-Sham orbitals ( 71 – 74 ) and is computationally less demanding compared to other approaches like constrained DFT ( 75 ) and excited-state force calculations ( 76 ). Nevertheless, it gives consistent phonon spectra compared with those obtained with constrained DFT ( 39 ), as shown in the Supplementary Materials.…”