Superconductivity modulated by structural phase transitions in pressurized vanadium-based kagome metals
Feng Du, Rui Li, Shuaishuai Luo, Yu Gong, Yanchun Li, Sheng Jiang, Brenden R. Ortiz, Yi Liu, Xiaofeng Xu, Stephen D. Wilson, Chao Cao, Yu Song, Huiqiu Yuan
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.