Using inhomogeneous dynamical mean-field theory, we show that the normal-metal proximity effect could force any finite number of Mott-insulating "barrier" planes sandwiched between semi-infinite metallic leads to become "fragile" Fermi liquids. They are fully Fermi-liquid-like at T=0, leading to a restoration of lattice periodicity at zero frequency, with a well-defined Fermi surface, and perfect (ballistic) conductivity. However, the Fermi-liquid character can rapidly disappear at finite omega, V, T, disorder, or magnetism, all of which restore the expected quantum tunneling regime, leading to fascinating possibilities for nonlinear response in devices.

The electronic and magnetic properties of ferromagnetic doped manganites are investigated by means of model tight-binding and self-interaction corrected local spin density ͑SIC-LSD͒ approximation calculations. It is found that the surface alone by breaking the cubic symmetry induces a difference in the occupation of the two e g orbitals at the surface. We found surface localization of one orbital and hence a change in the Mn valency from four in the bulk to three at the subsurface. Different surface or disordered interface induced localization of the orbitals are considered too with respect to the nature and the strength of the local orbital ordering and magnetic exchange coupling between the surface/interface and the bulklike region. We predict that better tunneling can be achieved in tunnel barriers that favor slightly the occupancy of the Mn e g͑3z 2 −r 2 ͒ at the interface.

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We report on first principles Self-Interaction Corrected LSD (SIC-LSD) calculations of electronic structure of LaMnO3 in the cubic phase. We found a strong tendency to localisation of the Mn eg electron and to orbital ordering. We found the ground state to be orbitally ordered with a staggered order of x 2 − z 2 and y 2 − z 2 orbits in one plane and this order is repeated along the third direction. The difference in energy with a solution consisting of the ordering of 3x 2 − r 2 and 3y 2 − r 2 is, however, very small. The system is in the insulating A-type antiferromagnetic ordered state in both cases. The presence of orbital ordering means breaking of the cubic symmetry and without recourse to distortion. The latter may rather be the result of the orbital ordering but the symmetry of this ordering is determined by coupling to the lattice. The strong tendency to localisation of the eg electron in LaMnO3 accounts for the survival of local distortions above the structural phase transition temperature.I.