We present direct imaging of magnetic flux structures over the $ab$ face of the anisotropic, spin-triplet superconductor ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ using a scanning $\mu \mathrm{SQUID}$ force microscope. Individual vortices with a single flux quantum were observed at low magnetic fields applied along the out-of-pane direction. At intermediate fields, the direct imaging revealed coalescing of vortices and the formation of flux domains. Our observations imply the existence of a mechanism in this material for bringing vortices together overcoming the conventional repulsive vortex-vortex interaction.

• Received 8 June 2004

DOI:https://doi.org/10.1103/PhysRevLett.95.097004