Magnetic field-induced abrupt enhancement in critical current density in LSMO/YBCO/LSMO/STO heterostructures

In this study, we report the influence of the complex coupling at the high-Tc-superconductor/oxide-ferromagnetic interface of LSMO/YBCO/LSMO trilayer heterostructures in terms of the superconducting critical current (I_c). We grew epitaxial tri-layer thin films by using the PLD technique, where LSMO bottom and top layer thicknesses were 10 nm and 15 nm, respectively, while the thickness of the middle YBCO layer was 15nm and 30 nm for the LY₁₅L and the LY₃₀L heterostructure respectively. In order to study the interface effect, the initial interface conditions (the work function difference, the orbital hybridization, and the magnetic coupling between the induced Cu and Mn moments) were preset by a cooling process with various field-cooled fields (FCF). In the FCF process, the sample was cooled down from 120K to 40K under a magnetic field parallel to the film surface and along the direction of the applied in-plane current. The I_c as a function of the FCF shows that I_c initially increases at lower FCF and attains maximum I_c at the intermediate range and then it starts to decrease with further increase in FCF. We observed the critical current I_c was greatly enhanced by ~18% at 0.5T for the LY₁₅L and ~90% at 0.6T for the LY₃₀L heterostructures. Moreover, we also observed the I_c increases with the increase in the applied magnetic field (AF) for the LY₁₅L heterostructure. This behavior is opposite to a normal superconducting system where I_c decreases with the increase in the applied magnetic field, and strongly implies the possible existence of triplet superconducting pairs at the interface and inside the FM layer. We proposed phenomenological and combination models which are based on singlet and triplet superconductivity mechanisms to explain the enhancement in critical current at the interface of LSMO/YBCO/LSMO heterostructures.