Bulk Superconductivity Induced by Se Substitution in Self-Doped BiCh₂-Based Compound CeOBiS_2−xSe_x

Investigation of Superconducting Properties and Possible Nematic Superconductivity in Self‐Doped BiCh2‐Based Superconductor CeOBiS1.7Se0.3

“…The CeOBiS 1.7 Se 0.3 single crystal crystallizes in the tetragonal space group P 4/ nmm and has lattice parameters of a = 4.0327(9) Å and c = 13.603(4) Å, which agrees with a report on the polycrystalline samples. [ 24 ] As demonstrated by Sogabe et al, [ 27 ] the bond valence sum (BVS) for Ce site was calculated using the following parameters: b 0 = 0.37 Å, R 0 = 2.151 Å for CeO bond, 2.62 Å for CeS bond, and 2.74 Å for CeSe bond. The bond distances between Ce and the nine coordinating anions were determined by single‐crystal X‐ray structural analysis.…”

“…The estimated valence of Ce is 3.25, which is consistent with the value obtained for the polycrystal and indicates that Ce has a mixed valence state. [ 24 ] Hence, the phase is a self‐doped system with mixed‐valence Ce.…”

“…The T c zero values are slightly higher than those observed for polycrystalline samples of CeOBiS 2− x Se x . [ 24 ] In the normal states, ρ c is clearly higher than ρ ab , which is due to the structure composed of stacking of electrically conductive BiCh 2 layers and insulating layers along the c axis. Similar behavior has been observed in various layered superconductors, such as Cu oxide Bi 2 Sr 2 CuO x , [ 28 ] Fe pnictide BaFe 2 As 2 , [ 29 ] and BiCh 2 ‐based compounds.…”

“…Notably, external elemental substitution is not needed to generate electron carriers in BiCh 2 layers because carriers are self‐doped via the mixed valence states of Ce. [ 24,25 ] This situation is clearly different from the cases of other RE(O,F)BiCh 2 systems, in which elemental substitutions are required for electron doping. [ 9,10 ] In addition, the Se concentration in the Bi‐Ch1 conducting plane is significantly lower than that in LaO 1− x F x BiSSe.…”

“…This study focused on the CeOBiS 2− x Se x system. Bulk superconductivity was observed in polycrystalline samples with x = 0.4 and 0.6 of CeOBiS 2− x Se x , and its T c was ≈3 K. [ 24 ] The crystal structure is composed of alternate stacks of a CeO blocking layer and a BiCh 2 conducting layer. Notably, external elemental substitution is not needed to generate electron carriers in BiCh 2 layers because carriers are self‐doped via the mixed valence states of Ce.…”