Enhanced conductance blockade due to Pauli exclusion in tunnel junctions with half-metallic electrodes

A defect-state mediated conductance blockade effect has been studied in magnetic tunnel junctions consisting of La0.7Sr0.3MnO3 (LSMO) electrodes and a SrTiO3 (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 washes out at higher temperature but it does not show strong dependence on magnetic field. 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. The result sheds new light on the half-metallic nature of LSMO.