Symmetry-dependent electron-electron interaction in coherent tunnel junctions resolved by measurements of zero-bias anomaly...

We provide experimental evidence that zero bias anomaly in the di↵erential resistance of magnetic tunnel junctions (MTJs) is due to electron-electron interaction (EEI). Magnon e↵ect is excluded by measuring at low temperatures down to 0.2 K and with reduced AC measurement voltages down to 0.06 mV. The normalized change of conductance is proportional to ln (eV /kB T ), consistent with the Altshuler-Aronov theory of tunneling with EEI but inconsistent with magnetic impurity scattering. The slope of the ln (eV /kB T ) dependence is symmetry dependent, i.e., MTJs with symmetry filtering show di↵erent slopes for P and AP states, while those without symmetry filtering (amorphous barriers) have nearly the same slopes for P and AP.