Superconductivity in Te-deficient polymorphic MoTe_2-x and its derivatives: Rich structural and electronic phase transitions

The group 6 transition metal dichalcogenides (TMDs) have been received great attentions due to intriguing superconducting states correlated with structural uncertainty and electronic complexity. Here, we synthesized Te-deficient polycrystals of semimetallic MoTe_2-x and its derivatives (Mo_1-y TM _yTe_2-x Ch _x(TM: Nb, Mn and V, Ch: P)), and investigated the structural and electronic phase transitions. It was found that all Te-deficient semimetallic phases (monoclinic 1T′, hexagonal 2H and rhombohedral 3R) exhibited the superconducting transition, in which 2H and 3R structures were evolved in Nb-substituted Mo_1-yNb_yTe_2-x (y = 0.4 for 2H, 0.6 for 3R), respectively. Moreover, we found that the superconducting state of 2H-and 3R-Mo_1-yNb_yTe_2-x appears at the vicinity of the transition from insulator to semimetal regime with the increased electron concentration via TM substitution and Te-deficiency. It is revealed that all superconducting 1T′-, 2H- and 3R-Mo_1-y TM _yTe_2-x Ch _x semimetals show the half-dome shaped superconducting phase diagram with respect to the electron concentration and TM substitution.