The superconducting order parameter and high-pressure studies of the V-based kagome materials AV3Sb5 (A=K, Rb, Cs)

The kagome lattice exhibits intrinsic geometric frustration and has been an important platform for studying quantum magnetism. Kagome metals have recently attracted significant attention due to the presence and tuning of Dirac Fermions, flat bands, and van Hove singularities. In particular, the vanadium -based kagome metals AV3Sb5 (A = K, Rb, and Cs) host coexistent unconventional charge density waves (CDWs) and superconductivity (SC), stimulating a large amount of research into their physical properties and underlying mechanisms. This article reviews studies on the superconducting pairing symmetry, the interplay between SC and CDW, and high-pressure tuning of SC in AV3Sb5 compounds with a focus on work conducted at the Center for Correlated Matter at Zhejiang University. These studies show that CsV3Sb5 exhibits nodeless SC regardless of whether SC coexists with CDW and that the superconducting gap size is highly sensitive to pressure or strain. Under hydrostatic pressure, the CDW in AV3Sb5 is gradually suppressed with increasing pressure, clearly revealing a competition with SC without signatures of a CDW quantum critical point. After the CDW in AV3Sb5 is fully suppressed with pressure, a further increase in pressure leads to a nonmonotonic evolution of the superconducting transition temperature driven by structural modulations, resulting in a superconducting dome at high pressures. Based on these results, we discuss the commonalities of the AV3Sb5 system and the issues to be addressed.