Nanocomposites and nanomaterials

Equal-spin Andreev reflection and long-range coherent transport in Josephson high-temperature superconductor/half-metallic ferromagnet nanocomposites
Krivoruchko V.N., Tarenkov V.Yu.
Donetsk Institute for Physics and Engineering, the NAS of Ukraine. Prospect Nauki, 46, Kyiv-03028, Ukraine. 
E-mail: krivoruc@gmail.com

In this report, random nanocomposites of half-metallic ferromagnet (hmF) (20–30nm of manganite La0.6Sr0.4MnO3 or La0.6Ca0.4MnO3 nanoparticles) and d-wave superconductor (SC) (5–10µm of Bi2Sr2Ca2Cu3O6+x particles, TC = 110K) with different components weight ratios have been studied. Transport characteristics of the 3D Josephson matter and a type of superconductivity have been studied. A spectroscopic (point-contact spectroscopy) signature of unconventional superconducting state is directly detected in the nanocomposites. We found the equal-spin Andreev reflection that unambiguously demonstrates the triplet long-range superconducting correlations in the nanocomposites. The sets of the experimental facts obtained cannot be explained on the basis of conventional models of the proximity effect in d-wave SC/hmF interfaces. The observed anomalies have a natural and qualitative explanation within a scenario of latent high-TC superconductivity in doped manganites [1,2] generalized, in our case, by the SC with d-wave pairing symmetry. The unusual transport properties of this type of nanocomposites bear much fundamental interest and make their promise for applications in superconducting spintronics, e.g. as a functional material in devices of superconducting supercomputers and telecommunications. 
The work was supported by the Science and Technology Center in Ukraine and the National Academy of Science of Ukraine (project No: 6250).  

1.	Krivoruchko V., Tarenkov V., Triple-gap superconductivity of MgB2 - (La,Sr)MnO3 composite. // Phys. Rev. B -2012. - 86, N 10.-P.104502(11).
2.	Krivoruchko V., D’yachenko A., Tarenkov V. Andreev-spectroscopy study of unconventional superconductivity in MgB2:(La,Sr)MnO3 nanocomposite. // Low Temp. Phys.-2014.- 40, N 10.-P. 1147–1154.