Pablo Aguado-Puente, Javier Junquera
At metal/insulator interfaces, the metallic wave functions with an energy eigenvalue within the band gap decay exponentially inside the insulator, creating a continuum of metal-induced gap states (MIGS). Despite being a genuine interface property, the features of MIGS have been typically discussed in terms of bulk Bloch functions of the insulator with an associated complex wave vector. We have developed a model to compare the energy-dependent decay factors obtained from the first-principles complex band structure of a bulk insulator (PbTiO3) and those coming from simulations of realistic capacitors, including explicitly the interface with the electrodes (Pt and SrRuO3). The agreement is very good, especially for the noble metal-based capacitor. For metal oxide electrodes, symmetry filtering arguments are required to understand the fine details. The ferroelectric polarization within the insulator layer tends to increase the effective decay factor, implying MIGS with shorter penetration lengths. These results are important in the design of giant tunnelling electroresistance and magnetoresistance devices with metal/oxide junctions.
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http://arxiv.org/abs/1303.4195
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