Probing Oxygen Content and Oxygen Isotope Effect in Manganite/Cuprate Heterostructures

It is believed that a long-range ferromagnet/superconductor proximity effect, involving odd-frequency pairing of spin triplets [1], exists in La_2/3Ca_1/3MnO₃/YBa₂Cu₃O_7-δ (LCMO/YBCO) heterostructures [2].  However, recent studies have shown that intergrowths and deoxygenation in the YBCO layer, induced by epitaxial strain from the LCMO layers, can also explain the anomalously long length scale of the critical-temperature (T_c) attenuation observed [3]. To shed crucial light on this problem, we carry out both x-ray absorption spectroscopy (XAS) and oxygen isotope effect (OIE) studies on LCMO/YBCO/LCMO trilayers grown by pulsed laser deposition. XAS is used to measure the YBCO oxygen content vs. layer thickness, thus determining the extent epitaxial strain deoxygenates YBCO. OIE is studied by measuring the T_c shift between ¹⁶O- and ¹⁸O- annealed samples of varying YBCO thickness, to asses whether the attenuated superconductivity in this system involves appreciable electron-phonon coupling [4]. These measurements allow us to rule out magnetism as playing a significant role in the observed proximity effect of LCMO/YBCO heterostructures.

[1]P. Lee et. al, PRB103 (2021)

[2]C.Visani et. al, Nat.Phys.8 (2012)

[3]H.Zhang et. al, APL103 (2013); ibid, arXiv:1710.10668v1

[4]G.Zhao et. al, PRB51 (1995)