Normal-Superfluid Interface Scattering For Polarized Fermion Gases

We argue that, for the recent experiments with imbalanced fermion gases, a temperature difference may occur between the normal (N) and the gapped superfluid (SF) phase. Using the mean-field formalism, we study particle scattering off the N-SF interface from the deep BCS to the unitary regime. We show that the thermal conductivity across the interface drops exponentially fast with increasing $h/k_B T$, where $h$ is the chemical potential imbalance. This implies a blocking of thermal equilibration between the N and the SF phase. We also provide a possible mechanism for the creation of gap oscillations (FFLO-like states) as seen in recent studies on these systems.Comment: 4 pages, 3 figure

Non local Andreev reflection in a carbon nanotube superconducting quantum interference device

We investigate a superconducting quantum interference device (SQUID) based on carbon nanotubes in a fork geometry [J.-P. Cleuziou {\it et al.}, Nature Nanotechnology {\bf 1}, 53 (2006)], involving tunneling of evanescent quasiparticles through a superconductor over a distance comparable to the superconducting coherence length, with therefore ``non local'' processes generalizing non local Andreev reflection and elastic cotunneling. Non local processes induce a reduction of the critical current and modify the current-phase relation. We discuss arbitrary interface transparencies. Such devices in fork geometries are candidates for probing the phase coherence of crossed Andreev reflection.Comment: 13 pages, 8 figures, revised versio

Transport and spectroscopic properties of superconductor - ferromagnet - superconductor junctions of La1.9Sr0.1CuO4La_{1.9}Sr_{0.1}CuO_4 - La0.67Ca0.33MnO3La_{0.67}Ca_{0.33}MnO_3 - La1.9Sr0.1CuO4La_{1.9}Sr_{0.1}CuO_4

Transport and Conductance spectra measurements of ramp-type junctions made of cuprate superconducting $La_{1.9}Sr_{0.1}CuO_4$ electrodes and a manganite ferromagnetic $La_{0.67}Ca_{0.33}MnO_3$ barrier are reported. At low temperatures below $T_c$, the conductance spectra show Andreev-like broad peaks superposed on a tunneling-like background, and sometimes also sub-gap Andreev resonances. The energy gap values $\Delta$ found from fits of the data ranged mostly between 7-10 mV. As usual, the gap features were suppressed under magnetic fields but revealed the tunneling-like conductance background. After field cycling to 5 or 6 T and back to 0 T, the conductance spectra were always higher than under zero field cooling, reflecting the negative magnetoresistance of the manganite barrier. A signature of superparamagnetism was found in the conductance spectra of junctions with a 12 nm thick LCMO barrier. Observed critical currents with barrier thickness of 12 nm or more, were shown to be an artifact due to incomplete milling of one of the superconducting electrodes.Comment: 10 figure