The upper critical field in the BiCh2-based superconductors CeOBiS1.7Se0.3 and PrO0.5F0.5BiS2-xSex (x = 0, 0.3)
We report the upper critical field (Bc2) in the BiCh2-based superconductors CeOBiS1.7Se0.3 and PrO0.5F0.5BiS2-xSex (x = 0, 0.3). Single crystals of CeOBiS1.7Se0.3 and PrO0.5F0.5BiS2-xSex (x = 0, 0.3) were grown using the flux method. Single-crystal structural analysis revealed that the crystal structure at room temperature is tetragonal (P4/nmm). Through electrical resistivity and magnetization measurements, bulk superconductivity was observed in all samples. For CeOBiS1.7Se0.3, the in-plane Bc2 is smaller than the conventional orbital limit and Pauli limit, suggesting that ferromagnetic ordering, which has been observed in a related Ce-containing BiCh2-based compound, affects Bc2 and superconductivity. In contrast, high in-plane Bc2 was observed for PrO0.5F0.5BiS2-xSex (x = 0, 0.3). We propose that the in-plane Bc2 is enhanced by antisymmetric spin-orbit coupling, which arises from the lack of local inversion symmetry.