Superconductivity in the metastable 1T ' and 1T ''& phases of MoS2 crystals

摘要

Transition-metal dichalcogenides open novel opportunities for the exploration of exciting new physics and devices. As a representative system, 2H-MoS2 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 1T 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 1T', 1T&DPRIME, and 1T"' lattice structures, which hinder the broad applications of MoS2 in future nanodevices and optoelectronic devices. Using K-x (H2O)(y)MoS2 as the precursor, we have successfully obtained high-quality layered crystals of the metastable 1T"'-MoS2 with root 3a x root 3a superstructure and metastable 1T'-MoS2 with a x 2a superstructure, as evidenced by structural characterizations through scanning tunneling microscopy, Raman spectroscopy, and x-ray diffraction. It is found that the metastable 1T'-MoS2 is a superconductor with onset transition temperature (T-c) of 4.2 K, while the metastable 1T"'-MoS2 shows either superconductivity with T-c of 5.3 K or insulating behavior, which strongly depends on the synthesis procedure. Both of the metastable polytypes of MoS2 crystals can be transformed to the stable 2H phase with mild annealing at about 70 degrees C in He atmosphere. These findings provide pivotal information on the atomic configurations and physical properties of 1T polytypes of MoS2.