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

Abstract

We study normal state electrical, thermoelectrical, and thermal transport in polycrystalline BiS2-based compounds, which become superconducting by F doping on the O site. In particular, we explore undoped LaOBiS2 and doped LaO0.5F0.5BiS2 samples, prepared either with or without high-pressure annealing, in order to evidence the roles of doping and preparation conditions. The high-pressure annealed sample exhibits room temperature values of resistivity rho around 5 m Omega cm, Seebeck coefficient S around -20 mu V/K, and thermal conductivity kappa around 1.5 W/Km, while the Hall resistance R-H is negative at all temperatures and its value is -10(-8) m(3)/C at low temperature. The sample prepared at ambient pressure exhibits R-H positive in sign and five times larger in magnitude, and S negative in sign and slightly smaller in magnitude. These results reveal a complex multiband evolution brought about by high-pressure annealing. In particular, the sign inversion and magnitude suppression of R-H, indicating increased electron-type carrier density in the high-pressure sample, may be closely related to previous findings about change in lattice parameters and enhancement of superconducting T-c by high-pressure annealing. As for the undoped sample, it exhibits 10 times larger resistivity, 10 times larger vertical bar S vertical bar, and 10 times larger vertical bar R-H vertical bar than its doped counterpart, consistent with its insulating nature. Our results point out the dramatic effect of preparation conditions in affecting charge carrier density as well as structural, band, and electronic parameters in these systems

Pressure-induced phase transition inLa1−xSmxO0.5F0.5BiSFang1, Yazici2, White3 et al. 2015Phys. Rev. B181240View full textAdd to dashboardCite

“…12,19 Although the crystal structure of both the sample annealed at ambient pressure (AP) and the one synthesized under applied high pressure (HP) have the same space group P4/nmm, the strongly reduced lattice parameters a and c are considered to be related to the enhancement in T c of HP samples. 12,19,20 On the other hand, LaO 0.5 F 0.5 BiS 2 (AP), which has a low T c , undergoes a structural phase transition from tetragonal to monoclinic at a pressure of 0.7 GPa, and T c is enhanced to 10.7 K. 21 Similar abrupt increases in T c were also observed in the compounds LnO 0.5 F 0.5 BiS 2 (Ln = Ce, Pr, Nd), LaO 0.5 F 0.5 BiSe 2 , EuBiS 2 F and Eu 3 Bi 2 S 4 F 4 under pressure. [22][23][24][25][26] A gradual increase in T c up to 5.4 K was observed at ambient pressure in La 1−x Sm x O 0.5 F 0.5 BiS 2 with increasing Sm concentration until the solubility limit near x = 0.8.…”

Thermoelectric properties of new Bi-chalcogenide layered compounds

“…To discuss this assumption, we plotted the n and the S reported in Refs. 13,32,41,45, and 53 in Fig. 8.…”

“…Partial substitutions of the O site by F generate electron carriers in the BiS2 conducting layers, and the F-substituted LaO1-xFxBiS2 shows a superconducting transition at low temperatures [10]. We considered the LaOBiS2-based compounds could exhibit a high thermoelectric properties since we observed a low thermal conductivity in the LaO1-xFxBiS2 samples ( ~ 2 W/mK at 300 K) [13]. Thus, we measured high-temperature thermoelectric properties (, S, and PF) of LaO1-xFxBiS2 and investigated the effect of the F substitution (electron doping) to the thermoelectric properties [43].…”

“…2(c). Indeed, in the LaOBiS2 system, the electron doping obviously degrades the thermoelectric properties [13,43]. To enhance the thermoelectric performance (PF) in the LaOBiS2 system, decreasing  without degradation of the absolute S is required.…”

Anisotropic superconductivity in La(O,F)BiSeS crystals revealed by field-angle dependent Andreev reflection spectroscopy

“…Some of the members of this new family of superconductors display exceptional richness in their phase diagram where even apparently antagonistic phenomena like superconductivity and ferro magnetism coexist [19,20]. Transport measurements in presence of pressure reveal that the critical temperature of the BiS 2 based superconductors increase with pressure signifying the importance of the crystal structure for the occurrence of superconductivity [21][22][23]. Based on such measurements and pressure dependent structural analysis it has been thought that superconductivity in this system might be governed by lattice expansion.…”