Superconductivity of Electron-Doped NdOBiS₂ by Substitution of Mixed-Valence Ce Ions

Abstract

Superconductivity is achieved in Nd 1−x Ce x OBiS 2 via electron doping using mixed-valence Ce ions. Single crystals with x = 0.2, 0.3, 0.4, and 0.5 are generated using a CsCl flux method. Plate-like single crystals with dimensions of 0.8×0.8×0.2 mm 3 were obtained. The magnetic susceptibility χ(T ) indicates large diamagnetism, and the electrical resistivity ρ(T ) indicates zero resistivity. The maximum value of T c is observed at 4.7 K in Nd 0.8 Ce 0.2 OBiS 2 from χ(T ). From the ρ(T ) measurements taken in several magnetic fields, the upper critical field µ 0 H c2 (0) is estimated to be ∼12 and ∼0.34 T for the ab-and c-planes, respectively. We redetermined µ 0 H c2 (0) of NdO 0.7 F 0.3 BiS 2 , as ∼35 and ∼0.78 T for the ab-and c-planes, respectively. The anisotropic parameter Γ is estimated to be ∼35 for Nd 0.7 Ce 0.3 OBiS 2 and ∼45 for NdO 0.7 F 0.3 BiS 2 . The µ 0 H c2 (0) of Nd 0.7 Ce 0.3 OBiS 2 is approximately two times smaller than that of NdO 0.7 F 0.3 BiS 2 , although the difference of Γ is approximately 10.

Growth and Characterization of ROBiS2 High-Entropy Superconducting Single Crystals

“…While the mixed entropy (Δ S mix ) value does not correlate with the superconducting transition temperature ( T c ) and superconducting anisotropy (γ s ), a decrease in mean R-site ionic radius leads to an increase in the chemical pressure, 8 , 9 which also increases T c and γ s . This trend is similar to that in the Ce 1– x Nd x OBiS 2 system, 40 , 41 in which the Δ S mix values are less than half (0.486 R –0.619 R ). Therefore, chemical pressure can affect the superconducting properties and has no significant effect on the high-entropy effect.…”

“…R-sites can affect the carrier concentration, chemical pressure, and high-entropy effect of the ROBiS 2 single crystals, that is, superconducting properties are affected by several parameters. Figure shows the mixed entropy (Δ S mix ) values, the mean R-site ionic radius, dependencies of superconducting transition temperature ( T c ), and superconducting anisotropy (γ s ) of ROBiS 2 (R = La + Ce + Pr + Nd + Sm) (HEA-type) and Ce 1– x Nd x OBiS 2 (R = Ce 1– x Nd x ) single crystals. , Owing to the comparable valence of Ce 3+ and Ce 4+ along with the slope of resistivity in the normal state region for samples A, B, and D, these carrier concentrations are considered comparable. Therefore, the superconducting properties of A, B, and D can be dominated by either the chemical pressure or the high-entropy effect.…”

Investigation of Superconductivity in Ce-Doped (La,Pr)OBiS2 Single Crystals

“…On the other hand, one of the BiS 2 -based superconductors, CeOBiS 2 , exhibits superconductivity without F substitution owing to the valence fluctuation between Ce 3+ and Ce 4+ [12,13]. Thus, F-free ROBiS 2 compounds with partial Ce substitution at the R-site also become superconductors in the form of the (La,Ce)OBiS 2 [14], (Ce,Pr)OBiS 2 [15,16], (Ce,Nd)OBiS 2 [17], and (La,Ce,Pr,Nd,Sm)OBiS 2 [18] compounds. Moreover, R-site elements affect the superconducting transition temperature.…”

Hydrostatic Pressure Effect in Non-Doping LaOBiSSe and Hole-Doping La1−xSrxOBiS2

“…It is known that Se substitution at S sites can effectively increase the overlapping, and induces bulk superconductivity with the optimum Se content of LaO 0.5 F 0.5 BiSSe at T c of 4.1 K [3,9]. Various electron doping is known to incur superconductivity, and electron doping of the valence fluctuation of Ce 3+ /Ce 4+ effectively generates bulk superconductivity [12][13][14][15][16].…”