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Electronic reconstruction at an interface between a Mott insulator and a band insulator

Abstract

Surface science is an important and well-established branch of materials science involving the study of changes in material properties near a surface or interface. A fundamental issue has been atomic reconstruction: how the surface lattice symmetry differs from the bulk. ‘Correlated-electron compounds’ are materials in which strong electron–electron and electron–lattice interactions produce new electronic phases, including interaction-induced (Mott) insulators, many forms of spin, charge and orbital ordering, and (presumably) high-transition-temperature superconductivity1,2. Here we propose that the fundamental issue for the new field of correlated-electron surface/interface science is ‘electronic reconstruction’: how does the surface/interface electronic phase differ from that in the bulk? As a step towards a general understanding of such phenomena, we present a theoretical study of an interface between a strongly correlated Mott insulator and a band insulator. We find dramatic interface-induced electronic reconstructions: in wide parameter ranges, the near-interface region is metallic and ferromagnetic, whereas the bulk phase on either side is insulating and antiferromagnetic. Extending the analysis to a wider range of interfaces and surfaces is a fundamental scientific challenge and may lead to new applications for correlated electron materials.

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Figure 1: Ground-state phase diagram computed in Hartree–Fock approximation as a function of the on-site Coulomb interaction U and the inverse of the La layer number n.
Figure 2: Spin and orbitally resolved charge densities as function of transverse (001) coordinate z for heterostructure with one La layer.
Figure 3: Dependence of total and metallic-subband charge densities ntot(z), nmetallic(z) on transverse spatial coordinate z for heterostructure with 6 La layers and U = 10t.
Figure 4: Fermi surface contours as functions of momenta (px,py) in plane parallel to layers, for six-layer heterostructure, U = 10t.

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Acknowledgements

We thank M. Potthoff, G. Sawatzky, W. Ku, H. Y. Hwang, E. W. Plummer and D. R. Hamann for conversations and the US NSF and the JSPS for support.

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Correspondence to Andrew J. Millis.

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Okamoto, S., Millis, A. Electronic reconstruction at an interface between a Mott insulator and a band insulator. Nature 428, 630–633 (2004). https://doi.org/10.1038/nature02450

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