Superconducting phase diagrams of S-doped <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>2</mml:mn><mml:mi>H</mml:mi><mml:mtext>−</mml:mtext><mml:mi>Ta</mml:mi><mml:msub><mml:mi mathvariant="normal">Se</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> under hydrostatic pressure
Shuxiang Xu, Ziyi Liu, Pengtao Yang, Keyu Chen, Jianping Sun, Jianhong Dai, Yunyu Yin, Fang Hong, Xiaohui Yu, Mianqi Xue, Jun Gouchi, Yoshiya Uwatoko, Bosen Wang, Jinguang Cheng
Abstract
We report the hydrostatic pressure effect on the charge density wave (CDW) and superconductivity (SC) of single-crystal $2H\text{\ensuremath{-}}\mathrm{Ta}{\mathrm{Se}}_{2\text{\ensuremath{-}}x}{\mathrm{S}}_{x}$ by measuring the electrical resistivity and ac magnetic susceptibility under various pressures up to 12.5 GPa. Different from the previously reported phase diagrams of CDW and SC as a function of the Se/S substitution and/or the uniaxial pressure, the superconducting transition temperature (${T}_{\mathrm{c}}$) was found to increase monotonously with increasing the pressure at first and then reaches a maximum constant above a critical pressure ${P}_{\mathrm{c}}$. The maximal ${{T}_{\mathrm{c}}}^{\mathrm{max}}$ is nearly two times higher than the optimal ones via the S doping and decreases with further increasing the S-doping level. High-pressure ac magnetic susceptibility demonstrates that the superconducting volume quickly increases along with the gradual suppression of CDW and reaches nearly 1 above ${P}_{\mathrm{c}}$, which provides clear evidences for pressure-induced crossover from CDW to bulk SC. High-pressure x-ray diffraction proves that there is no structural phase transition in $2H\text{\ensuremath{-}}\mathrm{Ta}{\mathrm{Se}}_{2}$ up to 20 GPa; although the dependence of ${T}_{\mathrm{c}}$ on the volume shows distinct behaviors at the initial S doping and the applied physical pressure, they both collapse into a universal curve upon the further volume shrinkage. This indicates that both physical pressure and the S-doping-induced chemical pressure can melt CDW and enhance SC through lattice contraction consistently. In comparison with the effects of hydrostatic pressure, the S doping can destruct the CDW ground state faster due to the presence of chemical disorders, which also restrict the further enhancement of ${T}_{\mathrm{c}}$ after the collapse of CDW.