Superconductivity modulated by structural phase transitions in pressurized vanadium-based kagome metals

The interplay of superconductivity with electronic and structural instabilities on the kagome lattice provides a fertile ground for emergent phenomena. The vanadium-based kagome metals AV3Sb5 (A= K, Rb, Cs) exhibit superconductivity on an almost ideal kagome lattice, with the superconducting transition temperature Tc forming two domes upon pressure tuning. The first dome arises from the competition between superconductivity and a charge-density wave, whereas the origin for the second dome remains unclear. Herein, we show that the appearance of the second superconducting dome in KV3Sb5 and RbV3Sb5 is associated with transitions from hexagonal to monoclinic structures, evidenced by the splitting of structural peaks from synchrotron powder x-ray diffraction experiments and imaginary phonon frequencies in first-principles calculations. In KV3Sb5, the transition to an orthorhombic structure is further observed for pressure pâ 20 GPa, and is correlated with the strong suppression of Tc in the second superconducting dome. Our findings indicate that distortions of the crystal structure modulate superconductivity in AV3Sb5 under pressure, providing a platform to study kagome lattice superconductivity in the presence of multiple electronic and structural instabilities.