Nodeless two-gap superconductivity revealed by low-temperature specific heat and lower critical field in 4Ha−NbSe2

Abstract

4Ha−NbSe2 single crystals were grown by the chemical vapor transport method followed by a quench to room temperature. The temperature-dependent magnetization and in-plane resistance reveal that the sample exhibits both charge-density-wave and superconducting orders, condensing at TCDW∼43 K and Tc∼6.5 K, respectively. The superconductivity was studied by specific heat and lower critical field (Hc1) down to 0.5 and 0.4 K, respectively. The electronic specific heat at superconducting state could be well described by an isotropic two-gap BCS model. The superconducting gaps were obtained to be of ΔL=1.1 meV and ΔS=0.3 meV with the weighting factors as 0.938 and 0.062, respectively. The in-plane Hc1//ab(T) and out-of-plane Hc1//c(T) also support the two-gap s+s–wave scenario, which derives Hc1//ab(0) and Hc1//c(0) as 78.3 and 149.8 Oe, respectively. The anisotropic parameter at 0 K based on Hc1 [ΓHc1(0)] was deduced to be ∼1.9. Our results reveal nodeless two-gap pairing symmetry in 4Ha−NbSe2, which would gain more insight into the superconductivity of TMDs.

Source-reported materials — not catalogue approval

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