Magnetic field effect in hybrid nanostructures

We examine the effect of the magnetic field on the proximity effect in nanostructures, self consistently using the Bogoliubov-deGennes formalism within the two dimensional extended Hubbard model. We calculate the local density of states and the pair amplitude. We study several nanostructures: superconductor - two dimensional electron gas, superconductor - ferromagnet. In these structures the magnetic field can be considered as a modulation parameter for the proximity effect.Comment: 9 pages, 9 figure

Superconductor-Ferromagnet Bi-Layers: a Comparison of s-Wave and d-Wave Order Parameters

We study superconductor-ferromagnet bi-layers, not only for s-wave but also for d-wave superconductors. We observe oscillations of the critical temperature when varying the thickness of the ferromagnetic layer for both s-wave and d-wave superconductors. However, for a rotated d-wave order parameter the critical temperature differs considerably from that for the unrotated case. In addition we calculate the density of states for different thicknesses of the ferromagnetic layer; the results reflect the oscillatory behaviour of the superconducting correlations.Comment: 11 pages, 5 figures, accepted for publication in J. Phys.: Condens. Matte

Order parameter oscillations in Fe/Ag/Bi2Sr2CaCu2O{8+delta} tunnel junctions

We have performed temperature dependent tunneling conductance spectroscopy on Fe/Ag/Bi2Sr2CaCu2O8 (BSCCO) planar junctions. The multilayered Fe counterelectrode was designed to probe the proximity region of the ab-plane of BSCCO. The spectra manifested a coherent oscillatory behavior with magnitude and sign dependent on the energy, decaying with increasing distance from the junction barrier, in conjunction with the theoretical predictions involving d-wave superconductors coupled with ferromagnets. The conductance oscillates in antiphase at E = 0 and E = +/-Delta. Spectral features characteristic to a broken time-reversal pairing symmetry are detected and they do not depend on the geometrical characteristics of the ferromagnetic film.Comment: 4 pages and 4 figures Submitted to Physical Review Letter

Temperature and Field Dependence of the Energy Gap of MgB2/Pb planar junction

We have constructed MgB2/Pb planar junctions for both temperature and field dependence studies. Our results show that the small gap is a true bulk property of MgB2 superconductor, not due to surface effects. The temperature dependence of the energy gap manifests a nearly BCS-like behavior. Analysis of the effect of magnetic field on junctions suggests that the energy gap of MgB2 depends non-linearly on the magnetic field. Moreover, MgB2 has an upper critical field of 15 T, in agreement with some reported Hc2 from transport measurements.Comment: 5 pages, 5 figures. Submitted to Phys. Rev.

Thermodynamic properties of the spin-chain compound Pr3_{3}RuO7_{7}

We have measured the magnetic susceptibility ($\chi )$ and specific heat (c$_{\rm P})$ of single crystals of Pr$_{3}$RuO$_{7}$. The susceptibility indicates a Neel transition at T$_{\rm N }= 54$ K, with an unusually mean-field specific heat anomaly. While $\chi$ indicates that all intrinsic moments order at T$_{\rm N}$, a Schottky-like anomaly in c$_{\rm P}$ suggests that there remains a small crystal-field splitting between a magnetic and non-magnetic state of the rare earth ions