Monolayer transition metal dichalcogenides (TMDCs) exhibit a large degree of polymorphism in crystal structures (2H, 1T and 1T') leading to a wide array of differing physical and chemical properties.

Two stable (2H and 1T') and one metastable (2H*) atomic structures of the MoTe₂ monolayer crystal

A collaborative effort from University of Southern California, Rice University and SLAC have identified that strong optical excitations induce lattice instabilities in monolayer TMDC crystals that lead to formation of high-energy metastable crystal structures

Emergence of lattice instabilities (denoted by negative frequencies in the phonon band structure) due to optical excitation of the MoTe₂ monolayer

These metastable crystal structures provide low-energy pathways for phase transformations between the semiconducting and metallic polymorphs of TMDC, leading to the formation of lateral semiconducting-metallic heterojunctions, which are critical for 2D optoelectronic devices.

Energy barrier in the optically excited crystal (red) are much lower than those in the unexcited crystal (blue) suggesting a new pathway for phase transitions

Publications

1. Rapid semiconductor-to-metal phase transition in MoTe₂ monolayers enabled by electronic excitation. A. Krishnamoorthy, L. Bassman, R. Kalia, A. Nakano, F. Shimojo, P. Vashishta, Submitted

PIs involved in this research

• Aiichiro Nakano, Priya Vashishta (USC)
• Pulickel Ajayan (Rice)
• Uwe Bergmann, David Fritz (SLAC)