Superconducting gap structure in carrier doped BiCh₂-based layered superconductors: A μSR study

The layered bismuth oxy-sulfide materials, which are structurally similar to Fe-pnictides/chalcogenides and cuprates superconductors, have sparked a lot of interest in the physics of reduced-dimensional superconductors. The pairing symmetry of the recently discovered BiCh₂-based superconductor, La_1−xCe_xOBiSSe with x = 0.3, was investigated using zero-field and transverse field (TF) muon spin measurements, as well as using magnetization and resistivity measurements. Resistivity and magnetization data confirmed bulk superconductivity below 2.7 K for x = 0.3. The temperature dependence of the magnetic penetration depth has been determined from TF-μSR data, which can be described by an isotropic two-gap s+s wave model compared to a single gap s- or anisotropic s-wave model, which resembles with Fe-pnictides/chalcogenides and MgB₂. Furthermore, from the TF-μSR data, we have determined the London's penetration depth λ_L(0) = 452(3) nm, superconducting carrier's density n_s = 2.18(1) × 10²⁶ carriers/m³ and effective mass enhancement m^∗ = 1.66(1) m_e, respectively. No signature of spontaneous internal field is found down to 100 mK in ZF-μSR measurement, which suggests that time-reversal symmetry is preserved in this system.