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

Abstract

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 $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ ($A=$ K, Rb, Cs) exhibit superconductivity on an almost ideal kagome lattice, with the superconducting transition temperature ${T}_{\mathrm{c}}$ 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 ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$ and ${\mathrm{RbV}}_{3}{\mathrm{Sb}}_{5}$ 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 ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$, the transition to an orthorhombic structure is further observed for pressure $p\ensuremath{\gtrsim}20$ GPa, and is correlated with the strong suppression of ${T}_{\mathrm{c}}$ in the second superconducting dome. Our findings indicate that distortions of the crystal structure modulate superconductivity in $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ under pressure, providing a platform to study kagome lattice superconductivity in the presence of multiple electronic and structural instabilities.