Charge order landscape and competition with superconductivity in kagome metals

Abstract

Correlated electronic systems are naturally susceptible to develop collective, symmetrybreaking electronic phases as observed in Cu-and Fe-based high-temperature superconductors, and twisted Moiré superlattices. The family of kagome metals AV3Sb5 (A = K, Rb, Cs) is a recently discovered, rich platform to study many of these phenomena and their interplay. In these systems, three-dimensional charge order (3D-CO) is the primary instability that sets the stage in which other ordered phases emerge, including unidirectional stripe order, orbital flux order, and superconductivity. Therefore, determining the exact nature of the 3D-CO is key to capture the broader phenomenology in AV3Sb5. Here, we use high-resolution angle-resolved photoemission spectroscopy to resolve the microscopic structure and symmetry of 3D-CO in AV3Sb5. Our approach is based on identifying an unusual splitting of kagome bands induced by 3D-CO, which provides a sensitive way to refine the spatial charge patterns in neighboring kagome planes. Notably, we found a marked dependence of the 3D-CO structure on alkali metal and doping: the 3D-CO in CsV3Sb5 is composed of kagome layers with alternating Star-of-David and Tri-Hexagonal distortions, while KV3Sb5, RbV3Sb5, and Sn-doped CsV3Sb5 realize a staggered charge pattern breaking C6 rotational symmetry. These results establish the microscopic structure of 3D-CO and its evolution with chemical composition for the first time, providing fresh insights on the origin of the cascade of exotic electronic phases in AV3Sb5.

Surface-termination-dependent electronic states in kagome superconductors AV3Sb5 (A = K, Rb, Cs) studied by micro-ARPES

“…Therefore, the present observations of the absence of ε-band splitting in KV 3 Sb 5 and its presence in RbV 1 for summary of the present key results). In this regard, it is noted that, while we observed the ε-band splitting in RbV 3 Sb 5 , it was absent in a recent study by another group [49]. This difference implies that the type of 3D CDW at the surface is not robust even in the same material.…”

“…As demonstrated above, the slab calculation with the 1 × 1 structure shows a reasonable agreement with the experimental band structure in the Sb-terminated surface, whereas the calculation cannot reproduce the band splitting in the A-terminated surface. Since the splitting of the V-3d band is probably due to the out-of-plane unit-cell doubling and the resultant band folding along k z [48,49,68,70], the present result strongly suggests the formation of 2 × 2 × 2 CDW in the A-terminated surface and its suppression in the Sb-terminated one. While such termination/polaritydependent CDW was suggested in a previous ARPES on CsV 3 Sb 5 [48], the present result has clearly established the universality among AV 3 Sb 5 .…”

“…Present results also provide deeper insight into the nature of CDW. According to the model calculations for various types of 3D CDW [49,70], the ε band splits when the kagome layers with the star-of-David (SoD)type and tri-hexagonal (TrH)-type distortions are stacked alternately, whereas it does not split when the kagome layers have only SoD or TrH distortion. Therefore, the present observations of the absence of ε-band splitting in KV 3 Sb 5 and its presence in RbV 1 for summary of the present key results).…”

“…Possible key factors determining the type of 3D CDW are carrier/chemical doping, cooling speed, etc. [48,49,71].…”

“…Therefore, high-spatial-resolution ARPES is needed to elucidate the bulk and surface band structures and their relationship with the physical properties in AV 3 Sb 5 . However, such a study is scarce especially regarding the A-element dependence, despite the fact that the bulk CDW and surface stripe charge order show a strong A-element dependence [21,38,40,41,[45][46][47][49][50][51].…”