Time-reversal invariant and fully gapped unconventional superconducting state in the bulk of the topological Nb0.25Bi2Se3

Abstract

Recently, the niobium (Nb)-doped topological insulator Bi_2Se_3, in which the finite magnetic moments of the Nb atoms are intercalated in the van der Waals gap between the Bi_2Se_3 layers, has been shown to exhibit both superconductivity with T_c = 3 K and topological surface states. Here we report on muon spin rotation experiments probing the temperature-dependent of effective magnetic penetration depth Lambda_eff(T) in the layered topological superconductor candidate Nb_0.25Bi_2Se_3. The exponential temperature dependence of lambda_(eff)^(-2)(T) at low temperatures suggests a fully gapped superconducting state in the bulk with the superconducting transition temperature T_c = 2.9 K and the gap to T_c ratio 2Delta/k_BT_c = 3.95(19). We also revealed that the ratio T_c/lambda_(eff)^(-2) is comparable to those of unconventional superconductors, which hints at an unconventional pairing mechanism. Furthermore, time reversal symmetry breaking was excluded in the superconducting state with sensitive zero-field muSR experiments. We hope the present results will stimulate theoretical investigations to obtain a microscopic understanding of the relation between superconductivity and the topologically non-trivial electronic structure of Nb_0.25Bi_2Se_3.

arXiv comment9 pages, 5 figures

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• A comprehensive review on topological superconducting materials and interfaces
• Probing the superconducting gap structure in the noncentrosymmetric topological superconductor ZrRuAs
• Phonon-induced rotation of the electronic nematic director in superconducting Bi${}_2$Se${}_3$
• Unconventional pressure dependence of the superfluid density in the nodeless topological superconductor $\alpha$-PdBi${}_2$
• Anisotropic Upper Critical Field, Seebeck and Nernst Coefficient in Nb0.20Bi2Se3 Topological Superconductor
• Pauli paramagnetism of triplet Cooper pairs in a nematic superconductor
• Strain induced spin vortex and Majorana Kramer's pairs in doped topological insulators with nematic superconductivity
• How spectrum-wide quantum criticality protects surface states of topological superconductors from Anderson localization: Quantum Hall plateau transitions (almost) all the way down
• Time reversal invariant single gap superconductivity with upper critical field larger than Pauli limit in NbIr${}_2$B${}_2$
• Tailoring the normal and superconducting state properties of ternary scandium tellurides, Sc${}_{6}M$Te${}_2$ ($M=$ Fe, Ru and Ir) through chemical substitution
• Muon Knight shift as a precise probe of the superconducting symmetry of Sr${}_2$RuO${}_4$
• Anomalous Josephson Hall effect in doped topological insulators with the nematic superconductivity
• Interaction between spin and Abrikosov vortices in doped topological insulators