Spin-triplet electron transport in hybrid superconductor heterostructures with a composite ferromagnetic interlayer
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DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
SpinTriplet Electron Transport in Hybrid Superconductor Heterostructures with a Composite Ferromagnetic Interlayer A. E. Sheyermana,b, K. Y. Constantiniana, G. A. Ovsyannikova,c, Yu. V. Kislinskiia, A. V. Shadrina,b, A. V. Kalabukhovc, and Yu. N. Khaydukovd a Kotelnikov
Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Moscow, 125009 Russia Moscow Institute of Physics and Technology, Dolgoprudny, Moscow oblast, 141700 Russia c Chalmers University of Technology, Gothenburg, SE41296 Sweden d MaxPlanck Institute for Solid State Research, Stuttgart, D70569 Germany email: [email protected]
b
Received October 29, 2014
Abstract—Hybrid YBa2Cu3O7 – x/SrRuO3/La0.7Sr0.3MnO3/Au–Nb superconductor mesastructures with a composite manganite–ruthenate ferromagnetic interlayer are studied using electrophysical, magnetic, and microwave methods. The supercurrent in the mesastructure is observed when the interlayer thickness is much larger than the coherence length of ferromagnetic materials. The peak on the dependence of the critical current density on the interlayer material thickness corresponds to the coherence length, which is in qualitative agreement with theoretical predictions for a system with spittriplet superconducting corre lations. The magneticfield dependence of the critical current is determined by penetration of magnetic flux quanta and by the magnetic domain structure, as well as by the field dependence of disorientation of the magnetization vectors of the layers in the composite magnetic interlayer. It is found that the supercur rent exists in magnetic fields two orders of magnitude stronger than the field corresponding to entry of a magnetic flux quantum into the mesastructure. The current–phase relation (CPR) of the supercurrent of mesastructures is investigated upon a change in the magnetic field from zero to 30 Oe; the ratio of the sec ond CPR harmonic to the first, determined from the dependence of the Shapiro steps on the microwave radiation amplitude, does not exceed 50%. DOI: 10.1134/S1063776115050192
1. INTRODUCTION In 2001, it was shown theoretically that near the interface between a ferromagnet and a superconduc tor, triplet superconducting correlations (TSCs) with a nonzero spin projection occur in the ferromagnet near its interface with the superconductor along with con ventional (singlet) correlations when the magnetiza tion of the ferromagnet is spatially nonuniform [1, 2]. A distinguishing feature of TSCs is their insensitivity to the exchange field and their penetration to the bulk of the ferromagnet to distances typical of the normal (nonmagnetic) metal (up to 100 nm). The occurring TSCs were detected experimentally from the presence of supercurrent in the structure formed by two super conductors with singlet superconductivity, which are connected by a ferromagnetic interlayer with helical magnetization [3], and by a ferromagnetic film or nanowire with nonuniform magnetization at the inter faces wit
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