Evolution of superconducting and transport properties in annealed FeTe$_{1-x}$Se$_x$ (0.1 $\leq$ $x$ $\leq$ 0.4) multiband superconductors

TL;DR

This study explores how annealing affects the superconducting and transport properties of FeTe$_{1-x}$Se$_{x}$ single crystals, revealing high-quality, bulk superconductivity with robust critical current densities and doping-dependent charge carrier behavior.

Contribution

It provides new insights into the effects of oxygen annealing on the superconducting quality and transport properties of FeTe$_{1-x}$Se$_{x}$, demonstrating enhanced critical current densities and detailed carrier dynamics.

Findings

High critical current densities (>10^5 A/cm^2 at 2 K) indicate bulk superconductivity.

Anisotropy parameter remains between 2 and 3 near Tc across doping levels.

Charge carriers transition from hole-like to electron-like at low temperatures, with doping-dependent characteristic temperature.

Abstract

We investigated the superconducting and transport properties in FeTe$_{1-x}$Se$_{x}$ (0.1 $\leq$ $x$ $\leq$ 0.4) single crystals prepared by O$_2$-annealing. Sharp superconducting transition width observed in magnetization measurement and the small residual resistivity prove the high quality of the crystals. All the crystals manifest large, homogeneous, and isotropic critical current density \emph{J}$_c$ with self-field value over 10$^5$ A/cm$^2$ at 2 K. The large and field-robust critical current densities prove that the superconductivity in FeTe$_{1-x}$Se$_{x}$ (0.1 $\leq$ $x$ $\leq$ 0.4) is in bulk nature. The values of anisotropy parameter close to $T_c$ for crystals with different Se doping levels all reside in the range of 2 - 3. Hall coefficients $R_H$ keeps positive and almost constant value at high temperatures, followed by a sudden decreases before reaching $T$$_c$, which indicates that the electron-type charge carriers become dominant at low temperatures. Furthermore, the characteristic temperature for the sudden decrease in $R_H$ gradually increases with Se doping.