Evidence for a square vortex lattice in Sr2RuO4 by muon-spin rotation measurements

A muon-spin-rotation study of the Aux-line lattice in Sr2RuO4 is presented. For the field parallel to the crystallographic c-direction, the observed field distribution strongly indicates a square symmetry of the vortex lattice. We determine the value of the coherence length from the upper critical field and the Ginzburg-Landau parameter which is found to be kappa = 1.2(1) from the field distribution. This gives a value for the penetration depth of lambda = 185(15) nm. The temperature dependence of the penetration depth is measured.