| Summary: | In this work, we investigate effects of strong correlation to quantum transport from atomic first principles. In order to accomplish this task, we use a well established state-of-the-art formalism of quantum transport where density functional theory (DFT) is carried out within the Keldysh non-equilibrium Green's functions (NEGF). To deal with certain strong correlation phenomenon, we integrated an local density approximation plus Hubbard U (LDA+U) exchange-correlation potential into the existing NEGF-DFT formalism. The LDA+U potential correctly accounts for the electronic structure of correlated material. We will present the theory and numerical implementation associated with the NEGF-DFT-(LDA+U) in detail. Extensive tests on the well known correlated material FeO crystal have been carried out and results compared with previous literature as well as to experimental data. === We then apply our NEGF-DFT-(LDA+U) technique to investigate transport physics of spin resolved tunnelling in Fe/MgO/Fe magnetic tunnel junctions (MTJ). We found that interfacial oxygen atoms are enough to localise the 3d electrons of infacial Fe atoms due to strong correlation. This surprising result substantially changes quantum transport properties of the MTJ, in particular it reduces magnetic resistance ratio by about 33%. This strongly correlated physics is absent if the conventional local spin density approximation (LSDA) is used in the NEGF-DFT analysis. Results of LSDA and LDA+ U exchange-correlation potential will be compared. Furthermore, through investigating contributions to scattering states by various atomic orbitals, we clearly identify the reason why LDA+U changes quantum transport in both quantitative and qualitative ways. Finally, we believe this strongly correlated physics should be general in other MTJs involving different oxides.
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