Effect of high pressure annealing on the normal state transport of LaO0.5F0.5BiS2

TL;DR

This study investigates how high pressure annealing influences the electrical, thermoelectrical, and thermal transport properties of LaO0.5F0.5BiS2, revealing significant changes in charge carrier behavior and electronic structure.

Contribution

It demonstrates the impact of high pressure annealing on the transport properties and electronic structure of BiS2-based compounds, highlighting the role of preparation conditions in tuning superconducting and normal state behaviors.

Findings

High pressure annealing reduces resistivity and Hall resistance, indicating increased electron carrier density.

Sign inversion of Hall resistance suggests a multiband electronic structure affected by annealing.

Doped samples show much lower resistivity and carrier densities compared to undoped samples.

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 ro around 5 mohmcm, Seebeck coefficient S around -20 microV/K and thermal conductivity k around 1.5 W/Km, while the Hall resistance RH is negative at all temperatures and its value is -10-8 m3/C at low temperature. The sample prepared at ambient pressure exhibits RH 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 RH, 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 Tc by high pressure annealing. As for the undoped sample, it exhibits the 10 times larger resistivity, 10 times larger |S| and 10 times larger |RH| than its doped counterpart, consistently 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.