Superconducting gap structure in the electron doped BiS₂-based superconductor

The influence of electron doping on semimetallic SrFBiS₂ has been investigated by means of resistivity, zero and transverse - field (ZF/TF) muon spin relaxation/rotation (μSR) experiments. SrFBiS₂ is semimetallic in its normal state and small amounts of La doping results in bulk superconductivity at 2.8 K, at ambient pressure. The temperature dependence of the superfluid density as determined by TF-μSR can be best modelled by an isotropic s - wave type superconducting gap. We have estimated the magnetic penetration depth λ_L (0) = 1087 nm, superconducting carrier density n_s = 3.7×10²⁶carriers m^-3 and effective-mass enhancement m^∗ = 1.558 m_e. Additionally, there is no clear sign of the occurrence of spontaneous internal magnetic fields below T_c, which implies that the superconducting state in this material can not be categorized by the broken time-reversal symmetry which is in agreement with the previous theoretical prediction.