Three-Dimensional Charge Density Wave and Surface-Dependent Vortex-Core States in a Kagome Superconductor CsV3Sb5

Abstract

The transition-metal-based kagome metals provide a versatile platform for correlated topological phases hosting various electronic instabilities. While superconductivity is rare in layered kagome compounds, its interplay with nontrivial topology could offer an engaging space to realize exotic excitations of quasiparticles. Here, we use scanning tunneling microscopy to study a newly discoveredZ2topological kagome metalCsV3Sb5with a superconducting ground state. We observe charge modulation associated with the opening of an energy gap near the Fermi level. When across single-unit-cell surface step edges, the intensity of this charge modulation exhibits aπ-phase shift, suggesting a three-dimensional2×2×2charge density wave ordering. Interestingly, while conventional Caroli–de Gennes–Matricon bound states are observed inside the superconducting vortex on the Sb surfaces, a robust zero-bias conductance peak emerges that does not split in a large distance when moving away from the vortex center on the Cs2×2surfaces, resembling the Majorana bound states arising from the superconducting Dirac surface states inBi2Te3/NbSe2heterostructures. Our findings establishCsV3Sb5as a promising candidate for realizing exotic excitations at the confluence of nontrivial lattice geometry, topology and multiple electronic orders.

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Plain Language Summary

In recent years, “kagome metals” have leapt to the forefront of investigations into new and exotic electronic states. In these metals, atoms are arranged into layered sets of overlapping triangles—a lattice that resembles the Japanese kagome weaving pattern. Recently, researchers discovered a new family of kagome metals that exhibit a superconducting ground state. Investigations into these materials have also dropped hints at several other unusual electronic behaviors. One example is Majorana bound states, peculiar quasiparticles hosted in a particular class of materials called topological superconductors, which are proposed as a key ingredient for fault-tolerant quantum computation. Here, we present a scanning tunneling microscopy study of one of these new kagome superconductors and find clues for such exotic states.

In our scans of the kagome metalCsV3Sb5, we find a 3D charge density wave state, a repeating pattern in which electrons crowd together and spread apart. Inside the superconducting vortices, we observe a robust zero-energy quasiparticle state. The spatial characteristic of this zero-energy state is in sharp contrast to the normal bound states found in conventional superconductors but reminiscent of the Majorana bound states observed in topologically nontrivial superconductors. Detailed analysis further supports the presence of Majorana bound states in this compound.

Our findings are likely to stimulate interest in kagome superconductors as hosts of Majorana states.