Superconducting Proximity Effect in (110)-oriented Cuprate/Perovskite Heterostructures: a Scanning Tunneling Spectroscopy Study

Recent studies have reported a superconducting proximity effect (PE) in c-axis heterostructures of ferromagnetic manganites and superconducting YBa₂Cu₃O_7-δ (YBCO) up to ~1 μm [1]. Although this anomalously long-range PE has been attributed to spin-triplet pairing with d-wave symmetry, this interpretation remains controversial due to the presence of strain-induced intergrowths in these films [2] and since scanning tunneling spectroscopy (STS) has failed to observe any direct microscopic evidence [3]. Our study extends the prior works to epitaxial (110)-oriented La_2/3Ca_1/3MnO₃/YBCO bilayer thin films to take advantage of both the longer in-plane coherence length of YBCO and the presence of resonant d-wave Andreev bound states on (110) surfaces. We directly probed the PE length scale with STS by analyzing these states with different manganite layer thicknesses. Additionally, LaNiO₃/YBCO films were measured as a paramagnetic control. Our results are interpreted in light of these recent studies and discussed in terms of various mechanisms for singlet-to-triplet conversion.

[1] D. Sanchez-Manzano et al., Nat. Mater. 21 (2022).

[2] H. Zhang et al., Appl. Phys. Lett. 103 (2013).

[3] I. Fridman et al., Phys. Rev. B 84 (2011).