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

Bo Peng,Bowen Hou,Heyuan Zhu,Weiwen Chen,Bartomeu Monserrat,Zhi-Jun Qiu,Hongming Weng,Costas M Soukoulis,Hezhu Shao,Desheng Fu,Hao Zhang

doi:10.1038/s41699-020-0147-x

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.

Highlights

A photo-induced phase transition (PIPT), resulting from cooperative electron–lattice interactions through transiently changing the electronic states of the solid by photoexcitations[1], is completely different from thermally or pressure-induced phase transitions
Compared with the vast number of materials exhibiting thermodynamic phase transitions, there are still very few solids undergoing a PIPT, and many investigations currently focus on bulk crystals possessing one-dimensional (1D) correlated electron chains in which PIPTs may be triggered due to inherent instabilities caused by electron–electron and electron–lattice interactions in these quasi-1D systems[1,5]
We demonstrate that the phase transition of monolayer MoTe2 can be triggered by photoexcitation of carriers

Summary

INTRODUCTION

A photo-induced phase transition (PIPT), resulting from cooperative electron–lattice interactions through transiently changing the electronic states of the solid by photoexcitations[1], is completely different from thermally or pressure-induced phase transitions. The topological phase displays gate-tunable superconductivity, providing a new potential platform to realize Majorana bound modes[17,18] Despite all this progress, the microscopic nature of the PIPT remains unclear. A strain-induced phase transition has been observed in monolayer MoTe222,23; laser-induced thermal strain may contribute to the observed phase transition Another explanation is that it is the electronic excitation that plays a critical role in the phase transition[12,13]. We demonstrate that the phase transition of monolayer MoTe2 can be triggered by photoexcitation of carriers

Peng et al 2

RESULTS AND DISCUSSION

METHODS