Square vortex lattices for two-component superconducting order parameters

I investigate the vortex lattice structure of the Ginzburg-Landau free ener gy for a two component order parameter in the weak-coupling clean limit whe n the field is along the high-symmetry axis in a tetragonal crystal. It is shown that the vortex-lattice phase diagram as a function of the Ginzburg-L andau free-energy parameters includes phases with a hexagonal, centered rec tangular, rectangular, and square unit cells. It is also shown that the squ are vortex lattice has the largest region of stability, The field distribut ion of the square vortex lattice near H-c2 is determined and the applicatio n of this model to Sr2RuO4 is discussed. [S0163-1829(98)00845-5].