Nearly Isotropic superconductivity in (Ba,K)Fe2As2

TL;DR

This study reveals that (Ba,K)Fe2As2 exhibits nearly isotropic superconductivity, challenging the notion that high-temperature superconductivity requires layered, quasi-two-dimensional structures, and highlighting the three-dimensional electronic nature of iron-arsenide compounds.

Contribution

The paper demonstrates that (Ba,K)Fe2As2 has isotropic superconducting properties, contrasting with previous layered superconductors, due to its more three-dimensional electronic structure.

Findings

Superconductivity in (Ba,K)Fe2As2 is nearly isotropic.

The electronic structure of these compounds is more three-dimensional.

Reduced dimensionality is not necessary for high-temperature superconductivity.

Abstract

Superconductivity was recently observed in the iron-arsenic-based compounds with a superconducting transition temperature (Tc) as high as 56K [1-7], naturally raising comparisons with the high Tc copper oxides. The copper oxides have layered crystal structures with quasi-two-dimensional electronic properties, which led to speculations that reduced dimensionality (that is, extreme anisotropy) is a necessary prerequisite for superconductivity at temperatures above 40 K [8,9]. Early work on the iron-arsenic compounds seemed to support this view [7,10]. Here we report measurements of the electrical resistivity in single crystals of (Ba,K)Fe2As2 in a magnetic field up to 60 T. We find that the superconducting properties are in fact quite isotropic, being rather independent of the direction of the applied magnetic fields at low temperature. Such behaviour is strikingly different from all previously-known layered superconductors [9,11], and indicates that reduced dimensionality in these compounds is not a prerequisite for high-temperature superconductivity. We suggest that this situation arises because of the underlying electronic structure of the iron-arsenide compounds, which appears to be much more three dimensional than that of the copper oxides. Extrapolations of low-field single-crystal data incorrectly suggest a high anisotropy and a greatly exaggerated zero-temperature upper critical field.