Ferromagnetic SrRuO₃ thin-film deposition on a spin-triplet superconductor Sr₂RuO₄ with a highly conducting interface

Abstract

Ferromagnetic SrRuO3 thin films are deposited on the ab-surface of single crystals of the spin-triplet superconductor Sr2RuO4 as substrates using pulsed laser deposition. The films are under a severe in-plane compressive strain. Nevertheless, the films exhibit ferromagnetic order with the easy axis along the c-direction below the Curie temperature of 158 K. The electrical transport reveals that the SrRuO3/Sr2RuO4 interface is highly conducting, in contrast with the interface between other normal-metals and the ab-surface of Sr2RuO4. Our results will stimulate the investigations on proximity effects between a ferromagnet and a spin-triplet superconductor.Hybrid structures with ferromagnetic metals (FMs) and superconductors are fascinating systems exhibiting unconventional phenomena originating from competition and cooperation between the ferromagnetic order and superconductivity. In the past, two aspects of exotic behavior of the proximity effect between a FM and a spinsinglet superconductor (SSC) have been revealed. Firstly, the amplitude and phase of the spin-singlet order parameter spatially oscillates in the FM due to exchange interaction and even leads to a π-junction.1 The penetration length of this effect is intrinsically limited to the order of a few nanometers. Secondly, a spin-triplet pair amplitude emerges over a length of the order of a micrometer into the FM if suitable magnetic inhomogeneity is present at the FM/SSC interface.2-7 The resulting superconducting symmetry in the FM is spin-triplet s-wave and thus classified as odd-frequency pairing.8 To induce such a superconductivity into a ferromagnet, half metallic FM CrO 2 with multi-fold magnetic anisotropy, 3,6 or alternatively ferromagnetic multilayer X/Co/X, where X can be PdNi, CuNi, Ni, or Ho, with non-collinear magnetization, is used in the SSC/FM/SSC Josephson junctions. 4, 5, 7Another approach to realize novel superconducting junctions with FM is to use a spin-triplet superconductor (TSC) with multiple degrees of freedom of the order parameter.10-12 Indeed, it has been theoretically predicted that not only charge supercurrent but also spin supercurrent emerges at FM/TSC interface and both can be controlled by the magnetization direction in the FM relative to the direction of the spins of the spin triplet Cooper pairs.11 Thus, FM/TSC junctions, with both controllable charge and spin supercurrents, would initiate a new research area that can be termed as "Superspintronics".Most likely, Sr 2 RuO 4 (SRO214) exhibits the chiral pwave spin-triplet superconducting order parameter analogous to the superfluid 3 He-A phase. 13, 14 SRO214 has also been attracting much attention as one of the leading candidates for the topological superconductor. Recently, its topological nature has been investigated with superconducting junctions.15-17 The main challenge in realizing a FM/TSC junction is the availability of thin films of spin triplet superconductors. By overcoming the difficulty in growing high quality SRO214 films, superconductivity has finally been ...

Control of magnetism in singlet-triplet superconducting heterostructures

“…The strongest evidence for triplet superconductivity has emerged for Sr 2 RuO 4 15, 16 . Existence of very pure single crystals with the perovskite structure made this material a testbed for studying heterostructures based on triplet superconductivity 17,18 .…”

Observation of superconducting gap spectra of long-range proximity effect in Au/SrTiO3/SrRuO3/Sr2RuO4 tunnel junctions

“…Ferromagnetic SRO113 thin films are grown epitaxially by pulsed laser deposition on cleaved ab-surfaces of SRO214 substrates with a thickness of 0.5 mm and a surface area of 3×3 mm 2 (Further details in Ref. [12]). Immediately after the deposition of SRO113, a 2-nm-thick insulating STO layer followed by a Au(20nm)/Ti(5nm) capping layer, are deposited ex-situ by DC sputtering.…”

“…However, crucial concerns in using TSCs are, firstly, availability of handful amount of bulk TSCs, and secondly, their compatibility to form an electronically transparent interface with other materials. Recently, some of the present authors developed an epitaxial TSC/F heterostructure by growing ferromagnetic SrRuO 3 (SRO113) thin films on superconducting SRO214 substrates [12]. Furthermore, long-range spintriplet proximity effect induced into SRO113 [13] was ob- * E-mail:msa60@cam.ac.uk served.…”

Anomalous Josephson Hall effect in magnet/triplet superconductor junctions

“…[18][19][20] Also, a highly conducting interface between a ferromagnet SrRuO 3 and a triplet superconductor Sr 2 RuO 4 has been realized recently. 21 The Hall effect in ferromagnets has been discussed intensively in the context of anomalous Hall effect. 22 The anomalous Hall effect arises from non-trivial spin texture, which is associated with the spin Berry phase effect.…”