Oxide Heterostructures

Correlated electron systems could become the core of future electronics utilizing their novel properties such as high-Tc superconductivity in cuprates and colossal magnetoresistance effect in manganites. Therefore, a general understanding of the interface properties of the correlated-electron materials is of crucial importance because any electronic device has interfaces. Further, because of recent experimental development, atomically controlled multilayers of correlated electron materials are available. Such multilayers or heterosructres are also useful playgrounds to explore further exotic phenomena out of correlated electron systems. This includes a variety of symmetry breaking transitions originating from the strong correlation. It is the ultimate goal of this project to establish the theoretical background and fundamental understanding of the properties of correlated-electron heterostructures.

For heterostructures between a Mott insulator and a band insulator, emergence of electronic phases, which are different from the bulk, was proposed by S. Okamoto (in collaboration with Prof. Millis at Columbia University). Recently, we constructed band diagram for perovskite-type transition-metal oxides and predicted novel electron-doped superconductivity at cuprates/manganites interfaces [S. Yunoki, A. Moreo, E. Dagotto, S. Okamoto, S. S. Kancharla, A. Fujimori, Phys. Rev. B 76, 064532 (2007)].

Schematic band diagrams of LCO: La2CuO4 is a parent compound of hole-doped superconductors, SCO (NCO): Sm2CuO4 (Nd2CuO4) is a parent compound of electron-doped superconductors, Nb0:01-STO: 0.01 wt% Nb-doped SrTiO3, Nb0:05-STO: 0.05wt% Nb-doped SrTiO3, YBCO: YBa2Cu3Oy, and LSMO corresponds to La1-xSrxMnO3, i.e. a colossal magnetoresistance manganite. These results are based on diffusion voltage measurements and photoemission spectroscopy. The tops of valence bands (VB) and bottoms of conduction bands (CB) are indicated by solid lines, while chemical potentials are indicated by dashed lines. [for detail, see S. Yunoki et al., Phys. Rev. B 76, 064532 (2007)]