Thermal conductivity and annealing effects in the iron-based superconductor FeSe$_{0.3}$Te$_{0.7}$

TL;DR

This study investigates how annealing affects thermal conductivity and superconductivity in FeSe$_{0.3}$Te$_{0.7}$ crystals, revealing that annealing enhances bulk superconductivity and modifies quasiparticle behavior, with effects dependent on crystal thickness.

Contribution

It demonstrates that vacuum annealing removes excess Fe, enhances bulk superconductivity, and influences thermal conductivity behavior in FeSe$_{0.3}$Te$_{0.7}$ crystals, highlighting the importance of sample treatment.

Findings

Annealing enhances low-temperature thermal conductivity below T_c.

Bulk superconductivity appears only after annealing, especially in thinner crystals.

Excess Fe is removed by vacuum annealing, improving superconducting properties.

Abstract

Thermal conductivity measurements in magnetic fields have been carried out for FeSe$_{0.3}$Te$_{0.7}$ single crystals as-grown and annealed at 400 {\degree}C for 100 h in vacuum ($\sim$ 10$^{-4}$ Pa). It has been found that the thermal conductivity in the {\it ab}-plane, {\kab}, of the annealed crystal shows an enhancement at low temperatures just below the superconducting transition temperature, {\tc}, owing to the thermal conductivity due to quasiparticles, while {\kab} of the as-grown crystal does not. This suggests that FeSe$_{1-x}$Te$_{x}$ is a strongly correlated electron system. It has also been found that both the degree of the enhancement of {\kab} just below {\tc} and the behavior of the suppression of {\kab} by the application of magnetic field for the annealed crystal depend on the thickness of the crystal. These results indicate that bulk superconductivity is absent in the as-grown crystal, appears only in the surface area in the annealed-thick crystal and appears in the almost whole region in the annealed-thin crystal. It has been concluded that the excess Fe included in the as-grown crystal is removed from the surface through the vacuum-annealing.