Structural, electromagnetic and thermoelectric properties of Bi₄O₄S₃superconductor

Abstract

We report on the synthesis and extensive characterization of layered Bi 4 O 4 S 3 superconductor. This is the optimally doped sample with T c ~5. While the parent compound is found to be semiconducting, the electrical resistivity of Bi 4 O 4 S 3 exhibits T 2 dependence in a small temperature range between 25 and 50 K. The typical dome structure for variation of T c with dopant concentration is not observed. From the magneto-transport data H c2 for Bi 4 O 4 S 3 is estimated to be ~2.75T with WHH approximation and the corresponding coherence length is ~110Å. Support for multiband signatures is not seen from magneto-resistance data. RF susceptibility data fits well for S-wave isotropic gap with gap value higher than BCS strong coupling limit. Hall measurements confirm dominance of electronic transport with charge carrier density of 4.405×10 19 cm −3 at 10 K. The experimental value of Seebeck coefficient at 35K is well in accord with the calculated value deduced by using density of charge carriers from Hall experiments. The Sommerfeld constant γ is estimated to be ~ 1.113 mJ/K 2 mol. Evidence for thermally activated flux flow is observed and the pinning potential is found to scale as B -0.3 for B < 0.1T and B -1.99 for B > 0.1T.

Effect of high-pressure annealing on the normal-state transport ofLaO0.5F0.5BiS2

“…It can be seen that in all cases, the Seebeck coefficients are roughly linear with temperature, suggesting that the diffusive mechanism of charge carriers dominates. This result is in agreement with similar optimally doped compounds such as PrO 0.3 F 0.7 BiS 2 [25] but at odds with other BiS 2based superconductors, where nonmonotonic behavior with a pronounced minimum possibly related to a drag mechanism is observed [26]. Contrary to Hall resistance curves, the Seebeck coefficient curves are negative at all temperatures for all three samples.…”

“…From the fitting, values of the electron effective mass around m 0 (m 0 bare electron mass) are obtained, in agreement with Ref. [26].…”

Superconductivity in layered BiS2-based compounds

“…1(a), the layered crystal structure is composed of Bi 2 S 4 layers, Bi 2 O 2 layers, and SO 4 units. The pied, the atomic composition should be Bi 4 O 4 (SO 4 )Bi 2 S 4 , also denoted as Bi 6 O 8 S 5 , with unit cell parameters a = 3.965 (5) and c = 41.234(0) Å [55], which is an insulator according to band structure calculations [1,21]. Superconductivity in Bi 4 O 4 S 3 is induced by electron doping into the BiS 2 layers via the introduction of vacancies into the SO 4 sites.…”

Upper critical magnetic field of LnO${}_{0.5}$F${}_{0.5}$BiS2 (Ln = La, Nd) superconductors at ambient and high pressure

“…26,27 However, other studies on CeO 0.5 F 0.5 BiS 2 , Bi 4 O 4 S 3 , La(O,F)BiSSe, PrO 1−x F x BiS 2 , Sr 0.5 La 0.5 FBiS 2 show nearly linear T dependences of H c2 that can be described by Ginzburg-Landau theory. [28][29][30][31][32] The lowest temperature reached in these studies was ∼2 K, and it should be mentioned that the range of values for the superconducting transition temperatures for the BiS 2 -based compounds at zero magnetic field is 2-11 K. In the present study, the upper critical field in the vicinity of T c in zero magnetic field is nearly linear with T and can be fitted with the WHH equation. Since the chemical compositions and crystal structures of the BiS 2 -based compounds are very similar, it is possible that the previously reported H c2 vs. T curves would also deviate from the WHH model when extended to lower temperature.…”