Vortex Lattice Structures ofSr2RuO4

The vortex lattice structures of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ for the odd-parity representations of the superconducting state are examined. Particular emphasis is placed upon the two dimensional representation which is believed to be relevant to this material. It is shown that when the zero-field state breaks time reversal symmetry, there must exist two superconducting transitions when there is a finite field along a high symmetry direction in the basal plane. Also it is shown that a square vortex lattice is expected when the field is along the $c$ axis. The orientation of the square lattice with respect to the underlying ionic lattice yields information as to which Ru $4d$ orbitals are relevant to the superconducting state.