Field-induced hexagonal to square transition of the vortex lattice in overdoped La1.8Sr0.2CuO4

Abstract We report on a small angle neutron scattering study of the vortex lattice in overdoped La 2− x Sr x CuO 4 ( x =0.2) up to high magnetic fields (9.5 T) applied perpendicular to the CuO 2 planes. At low magnetic fields we observe a crossover from hexagonal to square coordination of the vortex lattice. This field-induced transition confirms the results obtained in slightly overdoped La 2− x Sr x CuO 4 ( x =0.17).