Anisotropic London Penetration Depth and Superfluid Density in Single Crystals of Iron-based Pnictide Superconductors

TL;DR

This study measures magnetic penetration depths in iron-based pnictide superconductors, revealing unconventional pairing behavior, small anisotropy, and the influence of multiband electronic structures and magnetic fluctuations.

Contribution

It provides detailed measurements of anisotropic penetration depths and analyzes their implications for pairing symmetry and electronic structure in iron-based superconductors.

Findings

Power-law behavior of penetration depth with exponent n=2-2.5

Small overall anisotropy, with 1111 system more anisotropic than 122

Evidence for complex multiband and magnetic fluctuation effects

Abstract

In- and out-of-plane magnetic penetration depths were measured in three iron-based pnictide superconducting systems. All studied samples of both 122 systems show a robust power-law behavior, $\lambda (T) T^n$, with the sample-dependent exponent n=2-2.5, which is indicative of unconventional pairing. This scenario could be possible either through scattering in a $s_{\pm }$ state or due to nodes in the superconducting gap. In the Nd-1111 system, the interpretation of data may be obscured by the magnetism of rare-earth ions. The overall anisotropy of the pnictide superconductors is small. The 1111 system is about two times more anisotropic than the 122 system. Our data and analysis suggest that the iron-based pnictides are complex superconductors in which a multiband three-dimensional electronic structure and strong magnetic fluctuations play important roles.