Functional Materials for Energy

Evidence for non-uniform superconductivity in iron-based materials

Figure 1: Temperature-dependence of magnetic susceptibility (χ) and electrical resistance (R) of Ca0.86Pr0.14Fe2As2, showing non-bulk superconductivity marked by weak diamagnetism (~ 6% at 2 K) and non-vanishing resistance (~10-6 ohm at 2 K).

Multi-scale bulk and local electronic and structural studies on an iron-based superconductor have revealed, for the first time, an origin of non-bulk superconductivity. Understanding the role of chemical doping in causing superconductivity can potentially lead to the design of advanced high-temperature superconductors (HTS).

‘Parent’ compounds of all known HTS are antiferromagnetic, and superconductivity is induced by chemical doping. In addition to introducing the charge carriers required for superconductivity, chemical doping is a potential source of electronic and structural non-uniformity and these effects, as well as the distribution of dopants in a material, have been unclear. Macro- and micro-scale measurements on single crystals of Pr0.14Ca0.86Fe2As2 have revealed that the non-bulk nature of the HTS state (see Fig. 1) is a consequence of non-uniform praseodymium distribution that develops localized, isolated superconducting regions within the crystals. Nano-scale electronic inhomogeneity exists in most of unconventional superconductors; in Pr0.14Ca0.86Fe2As2, however, the extent of inhomogeneity is exceptional and explains non-bulk superconducting response. Our results help to better understand the role of chemical doping and nature of pairing mechanism in unconventional HTS.

Krzysztof Gofryk, Minghu Pan, Claudia Cantoni, Bayrammurad Saparov, Jonathan E. Mitchell, and Athena S. Sefat,  “Local inhomogeneity and filamentary superconductivity in Pr-doped CaFe2As2,” Phys. Rev. Lett. 112, 047005 (2014).    DOI: 10.1103/PhysRevLett.112.047005

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