Search for spontaneous edge currents and vortex imaging in Sr₂RuO₄ mesostructures

Scanning Hall probe microscopy has been used to search for spontaneous fields at the well-defined edges of large mesoscopic disks, etched into the ab surface of very high quality single crystal Sr₂RuO₄. Such fields are predicted to exist at locations of broken translational symmetry as a consequence of the proposed two-component spin-triplet chiral order parameter dˆ = Δ₀(k_x ± ik_y ) zˆ. We find no evidence for such fields and impose an upper limit of ±2.5 mG on their magnitude. We do, however, observe an abrupt apparent loss of strong bulk pinning and a change in the screening behavior above H ∼ 25 Oe. At high fields (H >25 Oe) pronounced magnetic screening by the disks is very well described by a model containing only strong edge currents, and bulk critical currents do not appear to play a significant role. Our results are discussed in terms of relevant theoretical predictions.