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

Abstract

We provide conclusive experimental evidence that zero-bias anomaly in the differential resistance of magnetic tunnel junctions is due to electron-electron interaction (EEI), clarifying a longstanding issue. The magnon effect that caused confusion is now 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 /k B T ), consistent with the Altshuler-Aronov theory of tunneling that describes the reduction of density of states due to EEI, but inconsistent with magnetic impurity scattering. The slope of the ln (eV /k B T ) dependence is symmetry dependent: the slopes for parallel and antiparallel states are different for coherent tunnel junctions with symmetry filtering, while nearly the same for those without symmetry filtering (amorphous barriers). This observation may be helpful for verifying symmetry-preserved filtering in search of new coherent tunneling junctions, and for probing and separating electron Bloch states of different symmetries in other correlated systems.

Low frequency noise in asymmetric double barrier magnetic tunnel junctions with a top thin MgO layer

“…Figure 4(b) shows that log(ε) has a roughly linear dependence on cos(θ ). It is interesting to note that similar θ dependence is expected for conductivity of a standard SBMTJ: G = a cos(θ ) + b, [18] where θ is the angle between external magnetic field direction and free layer magnetization orientation, a and b are parameters related to the device. This may suggest an intrinsic correlation between spin rotation and magnetic losses and further investigation is required.…”

Unveiling the Mechanism for the Split Hysteresis Loop in Epitaxial Co2Fe1-xMnxAl Full-Heusler Alloy Films

“…In this paper, we identified the model which best describes the system by comparing the uniaxial anisotropy field and fourfold anisotropy field obtained with FMR and vibrating sample magnetometer (VSM) measurements on the Co 2 Fe 1- x Mn x Al films with different Mn concentrations. Co 2 Fe 1- x Mn x Al is a kind of Co-based full-Heusler alloys, which possess high spin polarization and have great potential in spintronics application 25 26 27 28 29 30 31 32 33 34 . Interestingly, electronic structure calculations have revealed that Co 2 MnAl can retain half-metallic property for different levels of Fe doping 35 36 .…”