Conductivity of the interface for spin-polarized electrons in the pseudogap state of underdoped YBa2Cu3Ox

We report resistance-temperature, conductance-voltage, and voltage-magnetic-field measurements in a range 4 of small-area junctions between colossal magnetoresistive materials and the high-temperature superconductor YBa2Cu3Ox (YBCO). We identify two forms of behavior. In one form the resistance of the junction falls with decreasing temperature and is associated with zero bias conductance peaks. In the other form the resistance rises below some characteristic temperature T*. In this latter case there is no zero bias conductance peak, but there are small peaks in the voltage-magnetic-field behavior below T*. We tentatively associate T* with the pseudogap temperature and argue that the observed effects result from an interaction between the spin-polarized current and the antiferromagnetic spin fluctuations of the pseudogap state.