Highly Robust Reentrant Superconductivity in CsV_3Sb_5 under Pressure

We present the superconducting (SC) property and high-robustness of structural stability of kagome CsV_3Sb_5 under in situ high pressures. For the initial SC-I phase, its T_\rm c is quickly enhanced from 3.5 K to 7.6 K and then totally suppressed at P \sim 10 GPa. With further increasing pressure, an SC-II phase emerges at P \sim 15 GPa and persists up to 100 GPa. The T_\rm c rapidly increases to the maximal value of 5.2 K at P=53.6 GPa and slowly decreases to 4.7 K at P=100 GPa. A two-dome-like variation of T_\rm c in CsV_3Sb_5 is concluded here. The Raman measurements demonstrate that weakening of E_\rm 2g mode and strengthening of E_\rm 1g mode occur without phase transition in the SC-II phase, which is supported by the results of phonon spectra calculations. Electronic structure calculations reveal that exertion of pressure may bridge the gap of topological surface nontrivial states near E_\rm F, i.e., disappearance of Z_2 invariant. Meanwhile, the Fermi surface enlarges significantly, consistent with the increased carrier density. The findings here suggest that the change of electronic structure and strengthened electron-phonon coupling should be responsible for the pressure-induced reentrant SC.