Observation of vortex coalescence, vortex chains and crossing vortices in the anisotropic spin-triplet superconductor Sr2RuO4

摘要

Scanning mu SQUID force microscopy is used to study magnetic flux structures in single crystals of the layered spin-triplet superconductor Sr2RuO4. Images of the magnetic flux configuration above the (a) over right arrow(b) over right arrow -face of the cleaved crystal are acquired, mostly after field-cooling the sample. For low applied magnetic fields, individual vortices are observed, each carrying a single quantum of flux. Above I G, coalescence of vortices is discovered. The coalescing vortices may indicate the presence of domains of a chiral order parameter. When the applied field is tilted from the (c) over right arrow -axis, we observe a gradual transition from vortex domains to vortex chains. The in-plane component of the applied magnetic field transforms the vortex domains to vortex chains by aligning them along the field direction. This behavior and the inter-chain distance varies in qualitative agreement with the Ginzburg-Landau theory of anisotropic 3D superconductors. The effective mass anisotropy of Sr2RuO4, gamma = 20, is the highest observed in three-dimensional superconductors. When the applied field is closely in-plane, the vortex form flux channels confined between the crystal-layers. Residual Abrikosov vortices are pinned preferentially on these channels. Thus the in-plane vortices are decorated by crossing Abrikosov vortices: two vortex orientations are apparent simultaneously, one along the layers and the other perpendicular to the layers. (C) 2007 Elsevier B.V. All rights reserved.