Unconventional superconductors with a multi-component order parameter support multiple phases of Abrikosov vortex lattices. A unique feature of superconductors with a multi-component order parameter is that a doubly quantized lattices may be stabilized at sufficiently high magnetic field. For two-dimensional irreducible representations of the hexagonal point group appropriate to UPt3 we find a vortex lattice transition between a an Abrikosov lattice of anisotropic, singly quantized vortices and a lattice of doubly quantized vortices. The observation of an Abrikosov lattice of doubly quantized vortices provides a unique signature of multi-component superconductivity. We also show that for doubly quantized vortices the current in the vortex core circulated in the opposite direction to the vortex currents outside the core.
Contributed Paper for the Proceedings of the 19th International Conference on Low Temperature Physics, Brighton, UK.