title: High-density two-dimensional small polaron gas in a delta-doped Mott insulator.
abstract: Heterointerfaces in complex oxide systems open new arenas in which to test models of strongly correlated material, explore the role of dimensionality in metal-insulator-transitions (MITs) and small polaron formation. Close to the quantum critical point Mott MITs depend on band filling controlled by random disordered substitutional doping. Delta-doped Mott insulators are potentially free of random disorder and introduce a new arena in which to explore the effect of electron correlations and dimensionality. Epitaxial films of the prototypical Mott insulator GdTiO3 are delta-doped by substituting a single (GdO)(+1) plane with a monolayer of charge neutral SrO to produce a two-dimensional system with high planar doping density. Unlike metallic SrTiO3 quantum wells in GdTiO3 the single SrO delta-doped layer exhibits thermally activated DC and optical conductivity that agree in a quantitative manner with predictions of small polaron transport but with an extremely high two-dimensional density of polarons, ~7 × 10(14) cm(-2).
authors.affiliation: Department of Physics, University of California, Santa Barbara, California.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Ouellette
authors.forename: Pouya
authors.initials: P
authors.lastname: Moetakef
authors.forename: Tyler A
authors.initials: TA
authors.lastname: Cain
authors.forename: Jack Y
authors.initials: JY
authors.lastname: Zhang
authors.forename: Susanne
authors.initials: S
authors.lastname: Stemmer
authors.forename: David
authors.initials: D
authors.lastname: Emin
authors.forename: S James
authors.initials: SJ
authors.lastname: Allen