Superconducting properties of YBCO/LaNiO₃ bilayers grown on (100) SrTiO₃ substrates

High-T_c superconducting YBa₂Cu₃O_y/ LaNiO₃ (YBCO/LNO) bilayers were grown by off axis magnetron sputtering on (100) SrTiO₃ substrates. Patterned samples with YBCO thicknesses of 50-100 nm and a fixed 20 nm LNO capping layer were measured with magnetic fields applied parallel to the c axis and within the ab plane. Relative to the well-studied single-layer YBCO, the bilayers exhibit a systematic suppression of superconductivity. Both the superconducting transition temperature (T_c) and the thermally activated flux-flow activation energy (U) decrease with decreasing YBCO thickness. The scaling of U(H) together with the temperature dependence of H_c2(T) near T_c is consistent with quasi-two-dimensional (2D) superconductivity confined at the YBCO/LNO interface. We attribute this behavior to interfacial strain- and redox-driven oxygen redistribution during LNO deposition, possibly accompanied by limited Ni intermixing, which together create a nanometer-scale region of reduced dimensionality and lower T_c. Interfacial superconductivity is established in oxide heterostructures and often shows quasi-2D behavior. Within this context, we present evidence consistent with quasi-2D behavior near T_c and discuss an interface-driven scenario in cuprate-nickelate bilayers. Given theoretical proposals that LaNiO₃ heterostructures could host nontrivial band topology under suitable conditions, these results motivate further tests for possible topological superconductivity in this platform.