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HL: Fachverband Halbleiterphysik

HL 12: 2D Materials I: Electronic Structure, Excitations, etc. (joint session O/CPP/HL)

HL 12.8: Vortrag

Montag, 16. März 2020, 12:30–12:45, WIL C107

Sub-picosecond photo-induced displacive phase transition in two-dimensional MoTe₂ — •Bo Peng^1,2, Hao Zhang², Heyuan Zhu², Bartomeu Monserrat¹, and Desheng Fu³ — ¹TCM Group, Cavendish Laboratory, University of Cambridge, United Kingdom — ²Department of Optical Science and Engineering, Fudan University, China — ³Department of Optoelectronics and Nanostructure Science, Shizuoka University, Japan

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. By first-principles calculations, we demonstrate that the PIPT in monolayer MoTe₂ from the semiconducting 2H phase to the topological 1T’ phase can be driven purely by electronic excitations. The photo-induced electronic excitation changes the electron density, and softens the lattice vibrational modes. These pronounced softenings lead to structural symmetry breaking within sub-picosecond timescales, which is far 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, corresponding to an 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.