Since the three dimensional (3D) Dirac semi-metal Cd 3 As 2 exists close to topological phase boundaries, in principle it should be possible to drive it into exotic new phases, like topological superconductors, by breaking certain symmetries. Here we show that the mesoscopic point-contacts between silver (Ag) and Cd 3 As 2 exhibit superconductivity up to a critical temperature (onset) of 6 K while neither Cd 3 As 2 nor Ag are superconductors. A gap amplitude of 6.5 meV is measured spectroscopically in this phase that varies weakly with temperature and survives up to a remarkably high temperature of 13 K indicating the presence of a robust normal-state pseudogap. The observations indicate the emergence of a new unconventional superconducting phase that exists only in a quantum mechanically confined region under a point-contact between a Dirac semi-metal and a normal metal. * These authors contributed equally to the work † ashok@chemistry.iitd.ac.in ‡ goutam@iisermohali.ac.in 1 arXiv:1410.2072v1 [cond-mat.supr-con]

CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (∼ 47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane is strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.

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We investigate the influence of a ferromagnetic layer (La 0.7 Sr 0.3 MnO 3 ) on the upper critical field of YBa 2 Cu 3 O 7−δ superconducting layer in a superconductor/ferromagnet (SC/FM) hybrid structure. The YBa 2 Cu 3 O 7−δ /La 0.7 Sr 0.3 MnO 3 (YBCO/LSMO) hybrid bilayers as well YBCO single layer were fabricated on (001) LaAlO 3 (LAO) substrate using pulsed laser deposition.The temperature dependent upper critical field ( ) B T c2of type-II superconductors are generally described in the frameworks laid down by Werthamer-Helfand-Hohenberg and Ginzburg-Landau. We employ both formalism to estimate ( ) B T c2 of YBCO from magneto-transport data in SC/FM bilayers of varying ferromagnetic layer thickness as well as for YBCO single layer. We find that the ( ) B T c2 of YBCO in YBCO/LSMO bilayer gets suppressed as compared to that of single YBCO layer. Further to this, we also observe that the ( ) B T c2 of YBCO in the bilayer system decreases with increasing ferromagnetic LSMO layer thickness. These two results are discussed in the light of magnetic proximity effect, spin-diffusion induced pair breaking and enhanced effective magnetic field experienced by the YBCO layer with increasing ferromagnetic LSMO layer thickness.

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