Mazin A. Khasawneh

Observation of spin-triplet superconductivity in co-based josephson junctions

We have measured a long-range supercurrent in Josephson junctions containing Co (a strong ferromagnetic material) when we insert thin layers of either PdNi or CuNi weakly ferromagnetic alloys between the Co and the two superconducting Nb electrodes. The critical current in such junctions hardly decays for Co thicknesses in the range of 12-28 nm, whereas it decays very steeply in similar junctions without the alloy layers. The long-range supercurrent is controllable by the thickness of the alloy layer, reaching a maximum for a thickness of a few nm. These experimental observations provide strong evidence for induced spin-triplet pair correlations, which have been predicted to occur in superconducting-ferromagnetic hybrid systems in the presence of certain types of magnetic inhomogeneity.

Spin-triplet supercurrent in Co-based Josephson junctions

In the past year several groups have reported experimental evidence for spin-triplet supercurrents in Josephson junctions containing strong ferromagnetic materials. In this paper we present several new experimental results that follow up on our previous work. We study Josephson junctions of the form S/X/N/SAF/N/X/S, where S is a superconductor (Nb), N is a normal metal, SAF is a synthetic antiferromagnet of the form Co/Ru/Co and X is an ferromagnetic layer necessary to induce spin-triplet correlations in the structure. Our work is distinguished by the fact that the generation of spin-triplet correlations is tuned by the type and thickness of the X layers. The most important new result reported here is the discovery that a conventional, strong ferromagnetic material, Ni, performs well as the X layer, if it is sufficiently thin. This discovery rules out our earlier hypothesis that out-of-plane magnetocrystalline anisotropy is an important attribute of the X layers. These results suggest that the spin-triplet correlations are most likely induced by noncollinear magnetization between the X layers and adjacent Co layers.

Spin-memory loss at Co/Ru interfaces

We have determined the spin-memory-loss parameter,

Critical current oscillations of elliptical Josephson junctions with single-domain ferromagnetic layers

\delta_{Co/Ru}

Josephson junctions with a synthetic antiferromagnetic interlayer

, by measuring the transmission of spin-triplet and spin-singlet Cooper pairs across Co/Ru interfaces in Josephson junctions and by Current-Perpendicular-to-Plane Giant Magnetoresistance (CPP-GMR) techniques. The probability of spin-memory loss at the Co/Ru interface is

Investigating the two-dimensional conductivity of CVD graphene using surface acoustic waves

(1-exp(-\delta_{Co/Ru}))

Critical Current Oscillations of Josephson Junctions with Ferromagnetic Layers

. From the CPP-MR, we obtain

Fabrication and characterization of single domain magnetic Josephson

\delta_{Co/Ru} = 0.34^{+0.04}_{-0.02}

Ferromagnetic Josephson Junctions for Cryogenic Memory

that is in good agreement with

Spin-triplet superconductivity induced by PdNi alloy in Co-based Josephson junctions

\delta_{Co/Ru} = 0.35 \pm 0.08