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

TL;DR

This study reveals that structural phase transitions in pressurized vanadium-based kagome metals modulate their superconducting properties, with new phases emerging under pressure linked to changes in superconducting behavior.

Contribution

It demonstrates the connection between structural phase transitions and the emergence of a second superconducting dome in pressurized vanadium-based kagome metals.

Findings

Second superconducting dome associated with structural transitions.

Structural distortions modulate superconductivity under pressure.

Transition to orthorhombic structure correlates with Tc suppression.

Abstract

The interplay of superconductivity with electronic and structural instabilities on the kagome lattice provides a fertile ground for the emergence of unusual phenomena. The vanadium-based kagome metals $A$V$_3$Sb$_5$ ($A=$ K, Rb, Cs) exhibit superconductivity on an almost ideal kagome lattice, with the superconducting transition temperature $T_{\rm c}$ 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 KV$_3$Sb$_5$ and RbV$_3$Sb$_5$ is associated with transitions from hexagonal $P6$/$mmm$ to monoclinic $P2$/$m$ structures, evidenced by splitting of structural peaks from synchrotron powder X-ray diffraction experiments and imaginary phonon frequencies in first-principles calculations. In KV$_3$Sb$_5$, transition to an orthorhombic $Pmmm$ structure is further observed for pressure $p\gtrsim20$ GPa, and is correlated with the strong suppression of $T_{\rm c}$ in the second superconducting dome. Our findings indicate distortions of the crystal structure modulates superconductivity in $A$V$_3$Sb$_5$ under pressure, providing a platform to study the emergence of superconductivity in the presence of multiple structural instabilities.