Evidence for two distinct anisotropies in the oxypnictide superconductors SmFeAsO_(0.8)F_(0.2) and NdFeAsO_(0.8)F_(0.2)

TL;DR

This study provides evidence for two different anisotropies in oxypnictide superconductors, indicating a possible new multi-band mechanism underlying their high-temperature superconductivity.

Contribution

It introduces a model distinguishing penetration depth and upper critical field anisotropies, revealing their distinct behaviors in oxypnictide superconductors.

Findings

Penetration depth anisotropy differs from upper critical field anisotropy.

Evidence of two distinct anisotropies in SmFeAsO and NdFeAsO superconductors.

Implication of a multi-band mechanism in oxypnictide superconductivity.

Abstract

Single crystals of the oxypnictide superconductors SmFeAsO_(0.8)F_(0.2) and NdFeAsO_(0.8)F_(0.2) with T_c in the range of 44 K to 48 K were investigated by torque magnetometry. An analysis of the data in terms of a recently proposed model for the anisotropic magnetization in the superconducting state, treating the penetration depth anisotropy differently than the upper critical field anisotropy, provides evidence that in the oxypnictide superconductors two distinct anisotropies are present. As a result the penetration depth anisotropy differs significantly in magnitude and in temperature dependence from the upper critical field anisotropy, analogous to MgB_2 but with a reversed sign of slope. This scenario strongly suggests a new multi-band mechanism in the novel class of oxypnictide high-temperature superconductors.