Magnetic proximity effect and superconducting triplet correlations at the cuprate superconductor and oxide spin valve interface

Abstract

A heterostructure consisting of a cuprate superconductor YBa 2 Cu 3 O 7-d and a ruthenate/manganite (SrRuO 3 /La 0.7 Sr 0.3 MnO 3 ) spin valve was studied using SQUID magnetometry, ferromagnetic resonance, and neutron reflectometry. It is shown that because of the magnetic proximity effect a magnetic moment is excited in the superconducting portion of the heterostructure, whereas the magnetic moment in the spin valve becomes suppressed. The experimentally obtained value of a typical penetration depth of a magnetic moment into the superconductor is significantly greater than the coherence length of the cuprate superconductor, which indicates that the induced magnetic moment mechanism of Cu atoms is dominant. The mesastructure prepared by adding niobium film as a second superconducting electrode to the existing heterostructure, exhibited a superconducting current (dc Josephson effect) at interlayer thicknesses that are much greater than the coherence length of the ferromagnetic materials. The maximum of the critical current density dependence on the thickness of the spin valve material corresponds to the interlayer coherence length, which agrees with the theoretical predictions associated with spin-triplet pairing. The superconducting current is observed at magnetic fields that are two orders of magnitude greater than the field corresponding to the occurrence of one magnetic flux quantum in the mesastructure. The ratio of the second harmonic of the current-phase dependence of the mesastructure superconducting current to the first, determined according to the dependence of the Shapiro steps on the amplitude of microwave exposure, did not exceed 50%. Published by AIP Publishing. [http://dx

Triplet Superconducting Correlations in Hybrid Superconducting Junctions

“…In this regard a composite manganite/ruthenate La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) interlayer, exhibiting non-collinear magnetization, looks promising for a triplet type Josephson junction. Indeed, this allowed us to observe for the first time a superconducting current though the composite LSMO/SRO interlayer, consisting of two functional oxides, and confirm the presence of spin-triplet component of the superconducting current [31][32][33][34][35][36].…”

Materials challenges for SrRuO3: From conventional to quantum electronics

“…This long-ranged proximity effect has been ascribed to crossed Andreev reflections taking place near domain walls at the SrRuO3/YBCO interface 142 or to resonant tunnelling of quasiparticles through an oxygen-depleted layer forming at the SrRuO3/YBCO interface 207 . It should be noted, however, than in hybrid metal/metal-oxide Nb/Au/La0.7Sr0.3MnO3/SrRuO3/YBCO JJs a long-ranged proximity effect is only observed when both ferromagnets (La0.7Sr0.3MnO3 and SrRuO3) are present 208 . The authors of ref.…”

“…The authors of ref. 208 relate this long-ranged proximity to the formation of spin-polarised (spin-triplet) Cooper pairs generated by a non-collinear magnetization 213 in the LSMO/SRO system.…”

“…Due to its lattice matching with other oxide perovskites including high-temperature superconductors (HTSs) like YBCO, SrRuO3 has been already studied in a variety of superconducting devices such as Josephson junctions [26][27][28]207,208 (JJs) and superconducting spin valves 209 . As a result of its good lattice matching with YBCO and thermal stability, it has also been shown that SrRuO3 can also be used as buffer layer to improve the performance of HTS coatings 210 and to boost their superconducting critical current (Ic) density.…”

“…26,28,207 ) and hybrid metal/metal-oxide JJs like Nb/Au/La0.7Sr0.3MnO3/SrRuO3/YBCO (ref. 208 ). Most of these experiments and independent low-T STS measurements on SrRuO3/YBCO bilayers 142 suggest that the superconducting order parameter can penetrate into SrRuO3 over a depth larger than 20 nm at 4.2 K (refs.…”