Tunneling, giant zero bias conductance, and polarized carriers injection from La2/3Ca1/3MnO3 epitaxial films

YBa₂Cu₃O_7-delta/La_1/3Ca_2/3MnO₃/La_2/3Ca_1/3MnO₃ junctions with nominal thicknesses of 100, 7, and 80 nm respectively were fabricated by dc sputtering technique and their electrical properties determined.The superconducting gap-like structure was observed, suggesting a transport mechanism via elastic tunneling. On the other hand, for junctions with a barrier resistance of 30 Omega a pronounced zero-bias conductance peak was obtained. The value of the conductance G (V = 0) decreased as the temperature was increased, which is an indication of the metallic-like behavior associated to the presence of pin-holes on the junction area. The spin-polarized carrier injection from the F layer through the AF layer provoked a strong reduction of the critical superconducting current with an efficiency as large as 1.4 at 15 K.