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Abstract:
Bilayers consisting of 4 unit cell (similar to 47 ) YBa2Cu3O7-d (YBCO) with 200 La (1-x) Ca (x) MnO3 (LCMO) on top were grown on SrTiO (3) substrates using pulsed laser deposition. The Ca concentration x of the LCMO layer was varied with x= 0.3, 0.45, 0.55 and 0.8. We observed that the superconducting transition temperature (T (C) ) is dependent on the Ca doping level and decreases as Ca concentration increases. Bilayers consisting of YBCO and antiferromagnetic insulating La Ca-0.2 0.8MnO (3) were not superconducting down to 4.2 K. A charge transfer mechanism cannot be responsible for this reduction of T (C) according to our analysis of the Fermi levels in YBCO and LCMO. It was revealed that T (C) is monotonically reduced as the in-plane lattice mismatch between YBCO and LCMO increases. Therefore we attribute the T (C) reduction in our bilayers to a structural origin, more specifically a large lattice mismatch enhances a creation of oxygen vacancies in YBCO and cation intermixing between YBCO and LCMO. A structural heterogeneity in YBCO/LCMO bilayers has an impact on its superconducting properties.
