Nodeless electron pairing in CsV${}_3$Sb${}_5$-derived kagome superconductors

Abstract

The newly discovered kagome superconductors represent a promising platform for investigating the interplay between band topology, electronic order, and lattice geometry. Despite extensive research efforts on this system, the nature of the superconducting ground state remains elusive. In particular, consensus on the electron pairing symmetry has not been achieved so far, in part owing to the lack of a momentum-resolved measurement of the superconducting gap structure. Here we report the direct observation of a nodeless, nearly isotropic, and orbital-independent superconducting gap in the momentum space of two exemplary CsV${}_3$Sb${}_5$-derived kagome superconductors -- Cs(V${}_{0.93}$Nb${}_{0.07}$)${}_3$Sb${}_5$ and Cs(V${}_{0.86}$Ta${}_{0.14}$)${}_3$Sb${}_5$, using ultrahigh resolution and low-temperature angle-resolved photoemission spectroscopy (ARPES). Remarkably, such a gap structure is robust to the appearance or absence of charge order in the normal state, tuned by isovalent Nb/Ta substitutions of V. Moreover, we observe a signature of the time-reversal symmetry (TRS) breaking inside the superconducting state, which extends the previous observation of TRS-breaking CDW in the kagome lattice. Our comprehensive characterizations of the superconducting state provide indispensable information on the electron pairing of kagome superconductors, and advance our understanding of unconventional superconductivity and intertwined electronic orders.

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• CsV${}_3$Sb${}_5$: a ${\mathbb{Z}}_2$ topological kagome metal with a superconducting ground state
• Unconventional Fermi surface instabilities in the Kagome Hubbard Model
• Unusual competition of superconductivity and charge-density-wave state in a compressed topological kagome metal
• Ironing out the details of unconventional superconductivity
• Nodal superconductivity and superconducting domes in the topological Kagome metal CsV3Sb5
• Effects, Determination, and Correction of Count Rate Nonlinearity in Multi-Channel Analog Electron Detectors

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• Probing the pairing symmetry in kagome superconductors based on the single-particle spectrum
• Observation of Anomalous Thermal Hall Effect in a Kagome Superconductor
• Charge density wave modulated third-order nonlinear Hall effect in 1$T$-VSe${}_2$ nanosheets
• Thermomodulated intrinsic Josephson effect in Kagome CsV3Sb5
• Local pairing versus bulk superconductivity intertwined by the charge density wave order in Cs(V${}_{1-x}$Ta${}_x$)${}_3$Sb${}_5$
• Inversion and Tunability of Van Hove Singularities in $A$V${}_3$Sb${}_5$ ($A$ = K, Rb, and Cs) kagome metals
• Impact of Charge Density Waves on Superconductivity and Topological Properties in AV${}_3$Sb${}_5$ Kagome Superconductors
• Stability Frontiers and Mixed-dimensional physics in the Kagome Intermetallics Ln3ScBi5 (Ln = La-Nd, Sm)
• Recent progress in quantum spin liquids, fractional magnetization plateaus, and unconventional superconductivity in kagome lattices
• Electronic inhomogeneity in Cs- and Sb-terminated surfaces of CsV${}_3$Sb${}_5$ probed by scanning photoemission spectromicroscopy
• Current-induced magnetoresistance hysteresis in the kagome superconductor CsV${}_3$Sb${}_5$
• Time-reversal symmetry-breaking phenomena in transport study of kagome superconductivity