Bulk evidence of anisotropic s-wave pairing with no sign change in the kagome superconductor CsV3Sb5

Abstract

The recently discovered kagome superconductors AV3Sb5 (A = K, Rb, Cs) exhibit unusual charge-density-wave (CDW) orders with time-reversal and rotational symmetry breaking. One of the most crucial unresolved issues is identifying the symmetry of the superconductivity that develops inside the CDW phase. Theory predicts a variety of unconventional superconducting symmetries with sign-changing and chiral order parameters. Experimentally, however, superconducting phase information in AV3Sb5 is still lacking. Here we report the impurity effects in CsV3Sb5 using electron irradiation as a phase-sensitive probe of superconductivity. Our magnetic penetration depth measurements reveal that with increasing impurities, an anisotropic fully-gapped state changes to an isotropic full-gap state without passing through a nodal state. Furthermore, transport measurements under pressure show that the double superconducting dome in the pressure-temperature phase diagram survives against sufficient impurities. These results support that CsV3Sb5 is a non-chiral, anisotropic s-wave superconductor with no sign change both at ambient and under pressure.

Charge-loop current order and Z3 nematicity mediated by bond order fluctuations in kagome metals

“…1 b, which is the even-parity modulation in the hopping integral (=real) 6 – 12 . Below the BO transition temperature T BO , superconductivity (SC) with highly anisotropic gap emerges for A = Cs 13 , 14 , and the gap structure changes to isotropic by introducing impurities. Also, nodal to nodeless crossover is induced by the external pressure in A = Rb,K 15 .…”

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“…The existence of residual zero energy states and the V -shaped superconducting gaps from the scanning tunneling microscopy (STM) experiment also seem to propose the existing of nodal points. However, the measurements of the spin-lattice relaxation rate, the magnetic penetration depth, the impurity effect, and the transport measurements indicate that the superconducting AV 3 Sb 5 is fully gapped [36][37][38][39][40][41]. Very recently, a nearly isotropic superconducting gap around the Fermi surface was revealed by the angle-resolved photoemission spectroscopy (ARPES) experiment, providing substantial evidence of a fully gapped superconducting state [42].…”

Nodeless Superconductivity in Kagome Metal CsV3Sb5 with and without Time Reversal Symmetry Breaking

“…Scanning tunneling microscopy (STM) has detected a V-shaped density of states, indicating a gapless superconductivity. ,, Furthermore, thermal conductivity shows a finite residual linear term in the 0 K limit, lending support to a nodal superconducting gap . On the other hand, the magnetic penetration depth revealed by both tunnel diode oscillator (TDO) and muon spin rotation (μSR) experiments suggests nodeless superconductivity in CsV 3 Sb 5 . − Moreover, from the spin–lattice relaxation measurement, a finite Hebel–Slichter coherence peak is observed just below T c , indicating a conventional s -wave pairing …”