Appearance of an inhomogeneous superconducting state in La_0.67Sr_0.33MnO₃-YBa₂Cu₃O₇-La_0.67Sr_0.33MnO₃ trilayers

Abstract

An experimental study of proximity effect in La_0.67Sr_0.33MnO₃-YBa₂CU₃O₇-La_0.67Sr_0.33MnO₃ trilayers is reported. Transport measurements on these samples show clear oscillations in critical current (I_c) as the thickness of La_0.67Sr_0.33MnO₃ layers (d_F) is scanned from ~50 Å to ~ 1100 Å. In the light of existing theories of ferromagnet-superconductor (FM-SC) heterostructures, this observation suggests a long range proximity effect in the manganite, modulated by its weak exchange energy (~2 meV). The observed modulation of the magnetic coupling between the ferromagnetic LSMO layers as a function of d_F, also suggests an oscillatory behavior of the SC order parameter near the FM-SC interface.