Improvement of superconducting properties in Fe1+xSe0.5Te0.5 superconductor by Cr-substitution

• All polycrystalline samples Fe1+xSe0.5Te0.5 (x=0, 0.01, 0.02) are grown via two step solid state reaction method.
• Hexagonal impurity phase formation starts as Cr-substitution increases more than 1 wt%.
• Superconducting diamagnetic fraction has been improved with Cr-substitution.
• High upper critical fields have been observed for Cr-sample.
• Correlation strength of Cooper pairs has been found stronger for Cr-sample.

Enhancement of superconducting transition temperature (Tc) of parent superconductor, Fe1+xSe, of ‘Fe-11’ family by Cr-substitution for excess Fe has been motivated us to investigate the effect of Cr-substitution in optimal superconductor of Fe1+xSe0.5Te0.5 at Fe site. Here, we report structural, magnetic, electrical transport, thermal transport and heat capacity properties of Cr-substitute compounds. x-ray diffraction measurement confirms the substitution of Cr-atoms in host lattice. Magnetic and electrical transport measurements are used to explore the superconducting properties where Cr-substituted compounds show improvement in superconducting diamagnetic fraction with same Tc as undoped one. Heat capacity measurement confirms the bulk superconducting properties of compounds. Thermopower measurement characterizes the type of charge carriers in normal state.