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 the emergence of unusual 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 P 6/mmm to monoclinic P 2/m structures, evidenced by splitting of structural peaks from synchrotron powder X-ray diffraction experiments and imaginary phonon frequencies in first-principles calculations. In KV3Sb5, transition to an orthorhombic P mmm structure is further observed for pressure p 20 GPa, and is correlated with the strong suppression of Tc in the second superconducting dome. Our findings indicate distortions of the crystal structure modulates superconductivity in AV3Sb5 under pressure, providing a platform to study the emergence of superconductivity in the presence of multiple structural instabilities.

Chiral excitonic order from twofold van Hove singularities in kagome metals

“…In the case of the vanadium metals AV 3 Sb 5 , we discuss a few relevant aspects of experiment. Superconductivity exists alongside density wave order which sets in at a higher temperature T * ≈ 90 K than superconductivity (T c ≈ 3.5 K) and appears to compete with superconductivity [24][25][26][27][28][29][30][31][32][33]. The Fermi surface is reconstructed by the presence of the density wave order, but DFT calculations and magnetotransport indicate that the roughly hexagonal Fermi contours hosting the twofold van Hove singularities remain in the reconstructed band structure, which mainly undergoes changes near the K points [49].…”

“…The application of c-axis pressure suppresses T * and increases T c [37][38][39][40][41][42][43][44]. Applied pressure should change the relative value of the intra/interflavour couplings by changing the separation of the two-dimensional layers, and also shifts the effective values of µ and δ [81].…”