Abstract
Transition-metal dichalcogenides open novel opportunities for the exploration of exciting new physics and devices. As a representative system, has been extensively investigated owing to its unique band structure with a large band gap, degenerate valleys, and nonzero Berry curvature. However, experimental studies of metastable polytypes have been a challenge for a long time, and electronic properties are obscure due to the inaccessibility of single phase without the coexistence of , , and lattice structures, which hinder the broad applications of in future nanodevices and optoelectronic devices. Using as the precursor, we have successfully obtained high-quality layered crystals of the metastable with superstructure and metastable with superstructure, as evidenced by structural characterizations through scanning tunneling microscopy, Raman spectroscopy, and x-ray diffraction. It is found that the metastable is a superconductor with onset transition temperature of 4.2 K, while the metastable shows either superconductivity with of 5.3 K or insulating behavior, which strongly depends on the synthesis procedure. Both of the metastable polytypes of crystals can be transformed to the stable phase with mild annealing at about 70 °C in He atmosphere. These findings provide pivotal information on the atomic configurations and physical properties of polytypes of .
- Received 3 September 2018
- Revised 21 October 2018
DOI:https://doi.org/10.1103/PhysRevB.98.184513
©2018 American Physical Society