Vortex studies in superconducting Ba(Fe0.93Co0.07)2As2

TL;DR

This study investigates vortex arrangements in superconducting Ba(Fe0.93Co0.07)2As2 using SANS and Bitter decoration, revealing highly disordered vortices due to strong pinning and providing insights into vortex lattice structure and disorder effects.

Contribution

First combined SANS and Bitter decoration analysis of vortex structures in Ba(Fe0.93Co0.07)2As2, highlighting disorder and vortex lattice characteristics.

Findings

Vortex configuration is highly disordered at all fields.

Vortex lattice shows distorted hexagonal symmetry with 6-fold coordination.

Scattered intensity decreases faster than expected from upper critical field estimates.

Abstract

We present small-angle neutron scattering (SANS) and Bitter decoration studies of the superconducting vortices in Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$}. A highly disordered vortex configuration is observed at all measured fields, and is attributed to strong pinning. This conclusion is supported by the absence of a Meissner rim in decoration images obtained close to the sample edge. The field dependence of the magnitude of the SANS scattering vector indicates vortex lattice domains of (distorted) hexagonal symmetry, consistent with the decoration images which show primarily 6-fold coordinated vortex domains. An analysis of the scattered intensity shows that this decreases much more rapidly than expected from estimates of the upper critical field, consistent with the large degree of disorder.