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Register a new userSpin-filtering in superconducting junction with the manganite interlayer
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Karen Constantinian
Publication date
2017
fields
Physics
and research's language is
English
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We report on the electronic transport and the impact of spin-filtering in mesa-structures made of epitaxial thin films of cuprate superconductor YBa2Cu3Ox(YBCO) and the manganite LaMnO3 (LMO) interlayer with the Au/Nb counterelectrode. Ferromagnetic resonance measurements of heterostructure Au/LMO/YBCO shows ferromagnetic state at temperatures below 150 K as in the case of reference LMO film grown on the neodymium gallate substrate. The heights of the tunneling barrier evaluated from resistive characteristics of mesa-structures at different thickness of interlayer showed an exponential decrease from 30 mV down to 5 mV with the increase of manganite interlayer thickness. Temperature dependence of the conductivity of mesa-structures could be described taking into account the d-wave superconductivity in YBCO and a spin filtering of the electron transport. Spin filtering is supported also by measurements of magneto-resistance and the high sensitivity of mesa-structure conductivity to weak magnetic fields.
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We investigate Magnetic Josephson Junction (MJJ) - a superconducting device with ferromagnetic barrier for a scalable high-density cryogenic memory compatible with energy-efficient single flux quantum (SFQ) circuits. The superconductor-insulator-superconductor-ferromagnet-superconductor (SISFS) MJJs are analyzed both experimentally and theoretically. We found that the properties of SISFS junctions fall into two distinct classes based on the thickness of S layer. We fabricate Nb-Al/AlOx-Nb-PdFe-Nb SISFS MJJs using a co-processing approach with a combination of HYPRES and ISSP fabrication processes. The resultant SISFS structure with thin superconducting S-layer is substantially affected by the ferromagnetic layer as a whole. We fabricate these type of junctions to reach the device compatibility with conventional SIS junctions used for superconducting SFQ electronics to ensure a seamless integration of MJJ-based circuits and SIS JJ-based ultra-fast digital SFQ circuits. We report experimental results for MJJs, demonstrating their applicability for superconducting memory and digital circuits. These MJJs exhibit IcRn product only ~30% lower than that of conventional SIS junctions co-produced in the same fabrication. Analytical calculations for these SISFS structures are in a good agreement with the experiment. We discuss application of MJJ devices for memory and programmable logic circuits.
The superconducting current has been observed in mesa-heterostructures Nb/Au/Sr2IrO4/YBa2Cu3Ox with Sr2IrO4 interlayer thickness d=5 and 7 nm and in-plane sizes L=10-50 mcm. A strontium iridate, Sr2IrO4, is known as a canted antiferromagnetic insulator at low temperatures and characterized also by the strong spin-orbit interaction due to the impact of the IrO2 plane. The superconducting critical current density jC =0.3 A/cm^2 for the case d=7 nm was observed at T=4.2K. The temperature dependences of the superconducting critical current IC(T) and the voltage position on the I-V curve of the gap singularity of the Nb electrode show an increase with decreasing temperature and corresponds to the expected BCS behavior of the Nb energy gap. The critical current is very sensitive to the influence of an external magnetic field and reduces twice at an external magnetic field (H=0.2 Oe for L=40-50 mcm) comparable with the earth magnetic field; The magnetic field dependence IC(H) at low H was narrower than the Fraunhofer pattern about 1.5 times. Both the integer and fractional Shapiro steps at voltages V=(m/n)(h/2e)fe were observed under microwave radiation at frequencies fe=38 GHz and fe=50 GHz. Fractional Shapiro steps (m/n=1/2, 3/2) may point on the presence of the second harmonic in the superconducting current-phase relation.
We study a superconducting hetro-junction with one side characterized by the unconventional chiral $p$-wave gap function $p_xpm ip_y$ and the other side the conventional $s$-wave one. Though a relative phase of $pm frac{pi}{2}$ between any two components of gap functions is favored in the junction region, mutual phase differences cannot achieve $pm frac{pi}{2}$ simultaneously, which results in frustration. Based on a Ginzburg-Landau free energy analysis, the frustrated pattern is determined to be $s+ ieta_1 (e^{ ieta_2 varphi/2}p_x +eta_3 e^{- ieta_2 varphi/2}p_y)$ with $eta_j=pm 1$ ($j=1,2,3$), where $varphi$ is the phase difference between the $p_x$- and $p_y$-wave gap functions. Furthermore, we find that the junction exhibits an anisotropic magnetoelectric effect, manifesting itself as an anisotropic spin magnetization along the edge of the junction.
We theoretically study spin current through ferromagnet (F) in a Josephson junction composed of s-wave superconductors and two layers of ferromagnets. Using quasiclassical theory, we show that the long-range spin current can be driven by the superconducting phase difference without voltage drop. The origin of this spin current is due to spin-triplet Cooper pairs (STCs) formed by electrons of equal-spin, which are induced by proximity effect inside the F. We find that the spin current carried by the STCs exhibits long-range propagation in the F even where the Josephson charge current is practically zero. We also show that this spin current persists over a remarkably longer distance than the ordinary spin current carried by spin polarized conduction electrons in the F. Our results thus indicate the promising potential of Josephson junctions based on multilayer ferromagnets for spintronics applications with long-range propagating spin current.
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