Superconductivity in doped FeTe1-xSx (x= 0.00 to 0.25) single crystals

TL;DR

This study synthesizes and characterizes FeTe1-xSx single crystals, revealing superconductivity at specific doping levels, with detailed structural, magnetic, and transport properties analyzed to understand the effects of sulfur substitution.

Contribution

First comprehensive analysis of superconductivity and structural properties in FeTe1-xSx single crystals across a range of sulfur doping levels.

Findings

Superconductivity observed at Tconset ~9.5K for x=0.10 and 8.5K for x=0.25.

High upper critical fields up to 60 Tesla for x=0.25.

Structural analysis shows lattice parameter decrease with S doping.

Abstract

We report self flux growth and characterization of FeTe1-xSx (x= 0.00 to 0.25) single crystal series. Surface X-ray diffraction (XRD) exhibited crystalline nature with growth in (00l) plane. Micro-structural (electron microscopy) images of representative crystals showed the slab-like morphology and near stoichiometric composition. Powder XRD analysis (Rietveld) of single crystals exhibited tetragonal structure with P4/nmm space group and decreasing a and c lattice parameters with increase in x. Electrical resistivity measurements (R-T) showed superconductivity with Tconset at 9.5K and 8.5K for x =0.10 and x =0.25 respectively. The un-doped crystal exhibited known step like anomaly at around 70K. Upper critical field Hc2(0), as calculated from magneto transport for x =0.25 crystal is around 60Tesla and 45Tesla in H//ab and H//c directions. Thermal activation energy [U0(H)] calculated for x =0.10 and 0.25 crystals followed weak power law, indicating single vortex pinning at low fields. Mossbauer spectra for FeTe1-xSx crystals at 300K and 5K are compared with non superconducting FeTe. Both quadrupole splitting (QS) and isomer shift (IS) for S doped crystals were found to decrease. Also at 5K the hyperfine field for x =0.10 superconducting crystal is decreased substantially from 10.6Tesla (FeTe) to 7.2Tesla. For x =0.25 crystal, though small quantity of un-reacted Fe is visible at room temperature, but unlike x =0.10, the low temperature (5K) ordered FeTe hyperfine field is nearly zero.