Abstract
The combination of non-trivial band topology and symmetry breaking phases gives rise to novel quantum states and phenomena such as topological superconductivity, quantum anomalous Hall effect and axion electrodynamics. Evidence of intertwined charge density wave (CDW) and superconducting order parameters has recently been observed in a novel kagome material AV3Sb5 (A=K,Rb,Cs) that features a Z2 topological invariant in the electronic structure. However, the origin of the CDW and its intricate interplay with topological state has yet to be determined. Here, using hard x-ray scattering, we demonstrate a three-dimensional (3D) CDW with 2*2*2 superstructure in (Rb,Cs)V3Sb5. Unexpectedly, we find that the CDW fails to induce acoustic phonon anomalies at the CDW wavevector but yields a novel Raman mode which quickly damps into a broad continuum below the CDW transition temperature. Our observations exclude strong electron-phonon coupling driven CDW in AV3Sb5 and point to an unconventional and electronic-driven mechanism that couples the CDW and the topological band structure.
Highlights
The charge density wave (CDW), a translational symmetry-breaking electronic fluid, plays a crucial role in unconventional superconductors and intertwined electronic orders [1,2,3,4,5]
While CDWs have been isolated from topological excitations, recently experimental evidence of a topological CDW with chiral flux has been observed in a new kagome metal AV3Sb5 (A 1⁄4 K, Rb, Cs) [6], whose crystal structure and 3D Brillouin zone are shown in Figs. 1(a) and 1(b), respectively
Interference effect, unconventional p-wave CDW and chiral flux phase have been theoretically predicted near the van Hove filling [4,9,10,11]
Summary
The charge density wave (CDW), a translational symmetry-breaking electronic fluid, plays a crucial role in unconventional superconductors and intertwined electronic orders [1,2,3,4,5]. Despite the intimate correlations between the CDW, superconductivity, and topological band structure [6,7,8,11,12,13,14,15,16,17,18], the nature of the CDW, in particular, its interplay with the lattice degree of freedom, remains largely unexplored This knowledge gap hinders the understanding of unconventional Fermi-surface instabilities in kagome metals near van Hove filling. Our results uncover the intriguing nature of the CDW phase in AV3Sb5 and shed light on the intertwined electronic and lattice instabilities in kagome metal near the van Hove filling. This result indicates that the STM-observed C6 symmetry breaking is likely a structural effect rather than electronic nematicity
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