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Understanding of surface and interface properties of correlated electron
materials
is an important scientific question and is necessary for possible
devices
utilizing these materials. In this talk we first present a general
discussion
of the issues likely to be relevant, including changes in lattice
structure,
interaction parameters, and electron density redistribution, and then
present recent results on the physics associated with charge
redistribution
in heterostructures,
inspired by a recent experiment on band insulator/Mott insulator
heterostructures performed by Ohtomo et al.[1], including
(1) Hartree-Fock analysis of a realistic three-band model for
LaTiO3/SrTiO3 heterostructure,
the structure grown and measured by Ohtomo et al.,[2]
(2) Dynamical-mean-field-theory (DMFT) analysis of a model
heterostructure
comprised of single-band Hubbard model.[3]
In each case, the heterostructure is defined by placing charge +1 at La
sites
(charge difference between La3+ and Sr2+ ions), and
the long-range Coulomb repulsion between conduction (Ti d) electrons
is treated by Hartree approximation.
We show that spin/orbital orderings in thin heterostructures are
generically different
from the bulk and that the interface region, ∼ 3 unit cell wide, is
always metallic.
Predictions for photoemission experiments are made to show
how the electronic properties change as a function of position through
the interface.
Optical conductivity measurements are proposed to investigate the nature
of orderings and
quasiparticle subbands. Preliminary results of magnetic phase diagram
computed by DMFT
as a function of layer thickness, interaction and temperature are
presented.[4] This work has been done in collaboration with Andrew J. Millis, and is supported by JSPS, NSF DMR 0338376 and DOE ER46169. [1]Ohtomo et al., Nature 419, 378 (2002). [2]Okamoto and Millis, Nature {\bf 428}, 630 (2004), and Phys. Rev. B 70, 195120 (2004). [3]Okamoto and Millis, Phys. Rev. B .70, 241104(R) (2004). [4]Okamoto and Millis (in preparation). |