Critical Fields and Anisotropy of NdO0.82F0.18FeAs Single Crystals

TL;DR

This study reports the growth of NdO0.82F0.18FeAs single crystals and investigates their anisotropy and critical magnetic fields, revealing unexpectedly low anisotropy and high upper critical fields, which are promising for applications.

Contribution

The paper provides the first measurements of anisotropy and critical fields in NdO0.82F0.18FeAs single crystals, showing lower anisotropy than theoretical predictions and high upper critical fields.

Findings

Anisotropy a 4.9, much lower than theoretical estimates.

Upper critical fields: H_{c2}^{H||ab} a 304 T, H_{c2}^{H||c} a 62-70 T.

Resistivity data up to 400 K show a curved temperature dependence.

Abstract

The newly discovered iron-based superconductors have stimulated enormous interests in the field of superconductivity. Since the new superconductor is a layered system, the anisotropy is a parameter with the first priority to know. Meanwhile any relevant message about the critical fields (upper critical field and irreversibility line) are essentially important. By using flux method, we have successfully grown the single crystals NdO0.82F0.18FeAs at ambient pressure. Resistive measurements reveal a surprising discovery that the anisotropy \Gamma = (mc/mab)^{1/2} is below 5, which is much smaller than the theoretically calculated results. The data measured up to 400 K show a continuing curved feature which prevents a conjectured linear behavior for an unconventional metal. The upper critical fields determined based on the Werthamer-Helfand-Hohenberg formula are H_{c2}^{H||ab}(T=0 K) = 304 T and H_{c2}^{H||c}(T=0 K)=62-70 T, indicating a very encouraging application of the new superconductors.