Abstract
A defect-state mediated conductance blockade effect has been studied in magnetic tunnel junctions consisting of La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) electrodes and a SrTiO$_3$ (STO) barrier. The blockade threshold is an order of
magnitude greater than the Coulomb charging energy estimated from the
conductance oscillations at low temperature. The blockade voltage decreases with the increase of the temperature or the magnetic field, whereas the Coulomb charging energy does not show strong dependence on either quantity.
An explanation is offered in terms of the spin blockade effect due to the
combination of the discrete Coulomb charging on the defect state in STO and the half-metallicity of the LSMO electrodes. This explanation sheds new light on the half metallic nature of LSMO.
