Abstract: We present electrical transport measurements in the superconducting dissipative state of crystalline iron deficient Fe 1−y Se samples. These iron deficient samples were synthesized using NaCl/KCl flux and are characterized by the presence of correlated defects. The dissipation in electrical transport experiments, when the driving current is perpendicular or parallel to the crystal planes, depends strongly on the direction of the applied magnetic field , ( H=12 T), within the sample plane. There is a dissipation modulation each 60∘ due to the presence of the correlated defects. We correlate these angular dependent features with the variation of the critical currents ( Jc ) changing the direction of H confined in the crystals planes. Jc was measured from magnetization loops at fixed temperatures and angles of H always within the basal planes.

Abstract: In this work, we study the electronic properties of FeSe/Fe3O4 bilayers deposited onto SrTiO3 (100) and MgO (100) substrates by DC magnetron sputtering. The comparative study of Fe3O4 films grown on SrTiO3 and MgO reveals significant differences in the intensity of the Verwey transition (Tv∼130K). This allows us to probe the impact of the distortions associated to the Verwey transition on the transport properties of the FeSe over-layer in the FeSe/Fe3O4 bilayers. A correlated increase in the resistance and weakened superconducting properties are observed..

Abstract: We present a comparative study of electrical transport properties in the normal state and in the dissipative superconducting state between pure TeX -FeSe phase and Fe deficient Fe TeX Se crystals. We discuss the influence of the intergrowth of the magnetic hexagonal phase (Fe TeX Se TeX ) in Fe deficient samples when compared to pure TeX -FeSe samples. In the superconducting state, we measured the TeX -plane electrical resistivity with magnetic field up to 16 T and the electrical resistivity as a function of the angle between the TeX axis and the applied field. The angular dependence at fixed temperature below the superconducting critical temperature, TeX , is very different for both sets of crystals. The Fe deficient samples display a vortex pinning-related feature at TeX 57 TeX off the plane while the pure TeX -FeSe phase samples show the persistence of a strong angular-dependent magnetoresistance characteristic of the normal state electronic structure.

Abstract: Penetration depth measurements show that thermal heat treatment in amorphous Zr70Cu30 induces a normal region 5000 Å thick at the surface of ultrarapid quenched ribbons. Upper critical field measurements indicate that the new induced phase is a normal one while the rest of the sample remains as a homogeneous superconducting phase.

Abstract: We investigate the connection between persistent illumination-induced effects in underdoped RBa2Cu3O7-delta known as persistent photoconductivity and Raman bleaching. Despite the long-standing assumption that the electrical and optical properties respond to the same light-induced change in the material, they have not been directly compared until now. We present a simultaneous experiment of Raman spectroscopy and electrical transport under visible illumination at low temperatures. The time dependence of the response in the two methods differs by two orders of magnitude, showing that the effects are connected but not identical. We discuss our results within the oxygen-vacancy reordering model of photobleaching and find that different Cu-O chain lengths affect the optical and the electrical response differently. Raman bleaching and persistent photoconductivity thus provide a different perspective on the microscopic oxygen vacancy distribution.