Nature of charge density waves and superconductivity in 1 T − TaSe 2 − x Te x

Transition-metal dichalcogenides (TMDs) $M{X}_{2}$ $(M=\text{Ti},\text{Nb},\text{Ta};X=\text{S},\text{Se},\text{Te})$ exhibit a rich set of charge density wave (CDW) orders, which usually coexist and/or compete with superconductivity. The mechanisms of CDWs and superconductivity in TMDs are still under debate. Here we perform an investigation on a typical TMD system, $1T\text{\ensuremath{-}}{\mathrm{TaSe}}_{2\ensuremath{-}x}{\mathrm{Te}}_{x}$ $(0\ensuremath{\le}x\ensuremath{\le}2)$. Doping-induced disordered distribution of Se/Te suppresses CDWs in $1T\text{\ensuremath{-}}{\mathrm{TaSe}}_{2}$. A domelike superconducting phase with the maximum ${T}_{\mathrm{c}}^{\mathrm{onset}}$ of 2.5 K was observed near CDWs. The superconducting volume is very small inside the CDW phase and becomes very large instantly when the CDW phase is fully suppressed. The observations can be understood based on the strong $q$-dependent electron-phonon coupling-induced periodic-lattice-distortion (PLD) mechanism of CDWs. The volume variation of superconductivity implies the emergence of domain walls in the suppressing process of CDWs. Our concluded scenario makes a fundamental understanding about CDWs and related superconductivity in TMDs.

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