Quasiparticle Transport Properties of d-Wave Superconductor/Ferromagnet/d-Wave Superconductor Junctions

Solving the time-dependent Bogoliubov-de Gennes equations, we calculate current-voltage characteristics (CVC) and conductances (G) of clean d-wave superconductor/ferromagnet/d-wave superconductor (DFD) junctions with transparent D/F interfaces. Due to the suppression of Andreev reflection (AR) by the exchange energy h in the ferromagnetic barrier and by the presence of gap nodes in the d-wave superconductor electrodes, there is a striking difference in shape and amplitude of CVC with respect to the case of isotropic s-wave superconducting banks. This provides an indication of the superconductor order parameter symmetry. The influence of AR is much better seen in the conductance dependence on the bias voltage G(V). The conductance curves have a rich nonlinear structure in lowvoltage multiple AR region. At higher voltages, the curves are almost flat, with characteristic dips located at eV 2 Delta(T) +/- h/n, with n = 1,2,...Delta(T) being the maximum order parameter at the temperature T. Observing these dips one could estimate the exchange energy h from experiment.