Study on the monolayer transition-metal ditellurides

Jinwoong Hwang

The layered transition metal dichalcogenides (TMDs), MX₂ (M = transition metal, X = S,  Se, Te), have become a paradigm material to study complex electronic phases in low dimensions, such as charge density wave, superconductivity, and topological orders. More outstanding properties, completely distinct from the bulk, have been reported, when the thickness of TMDs is reduced to the monolayer (ML), due to the absence of interlayer coupling and the resulting electronic structure, and symmetry changes. One of the less investigated ingredients in understanding the properties of ML TMDs or ML van der Waals (vdW) materials is how the varying interlayer coupling strength, e.g., as it increases going from S, Se to Te, affect the change of the material properties in ML limit. In general, the stronger interlayer coupling, the more dramatic changes are expected. However, the materials platform that shows such dramatic changes, close to the crossover from the vdW interaction to the covalent interaction, is rare due to the increasing difficulty in both exfoliation and vdW epitaxial growth as the interlayer interaction becomes stronger. 

In this talk, I will introduce recent studies of ML TMTe₂, which has the stronger interlayer coupling strength compared to the vdW interaction. The combining study of molecular beam epitaxial (MBE) growth and in-situ angle-resolved photoemission spectroscopy (ARPES) characterization clearly revealed that stronger Te-Te interlayer coupling significantly affects the quantum ground states of MTe₂.