2, Stanford University, Stanford, California, United States
Monolayers of transition-metal dichalcogenides (TMDs) exhibit numerous crystal phases with distinct structures, symmetries and physical properties. Exploring the physics of transitions between these different structural phases in two dimensions may provide a means of switching material properties, with implications for potential applications. Structural phase transitions in TMDs have so far been induced by thermal or chemical means; purely electrostatic control over crystal phases through electrostatic doping was recently proposed as a theoretical possibility, but has not yet been realized. Here we report the experimental demonstration of an electrostatic-doping-driven phase transition between the hexagonal and monoclinic phases of monolayer molybdenum ditelluride (MoTe2). And such phase transition shows a hysteretic loop in Raman spectra, and can be reversed by increasing or decreasing the gate voltage. By combining second-harmonic generation spectroscopy with polarization-resolved Raman spectroscopy, it shows that the induced monoclinic phase preserves the crystal orientation of the original hexagonal phase. This electrostatic-doping control of structural phase transition opens up new possibilities for developing phase-change devices based on atomically thin membranes.