Toward an artificial Mott insulator: Correlations in confined high-density electron liquids in SrTiO3

Abstract

We investigate correlation physics in high-density, two-dimensional electron liquids that reside in narrow SrTiO 3 quantum wells. The quantum wells are remotely doped via an interfacial polar discontinuity and the three-dimensional (3D) carrier density is modulated by changing the width of the quantum well. It is shown that even at 3D densities well below one electron per site, short-range Coulomb interactions become apparent in transport, and an insulating state emerges at a critical density. We also discuss the role of disorder in the insulating state.

Symmetry Lowering in Extreme-Electron-Density Perovskite Quantum Wells

“…The structure had a 10 nm SrTiO 3 buffer and cap, respectively. The SrTiO 3 quantum well thicknesses matched those in the electrical studies [10], except here they were in a single sample. This allowed for recording all data in a single session, thus reducing effects from any variability in microscope conditions.…”

“…Although the electrons are localized in the 1 SrO and 2 SrO quantum wells, Hall measurements indicate that these quantum wells still contain the entire electron density of $6 Â 10 14 cm 2 , or one electron shared between three TiO 2 planes in the 2 SrO layer quantum well [10,30,31]. Quantum wells with thicker SrTiO 3 , having a lower 3D electron density, are metallic [10].…”

“…This is remarkable because bulk SrTiO 3 is a band insulator with cubic symmetry. The thinnest quantum wells, which are 2 SrO layers wide on average, are insulating [10]. Recent density functional theory simulations indicate that oxygen octahedral tilts in the thinnest quantum wells are critical in promoting a Mott insulating state [11].…”

“…For example, SrTiO 3 can be electrostatically doped to high sheet carrier densities ($ 1=2 mobile electron per interface unit cell) by interfacing it with a rare earth titanate [7][8][9]. Signatures of electron correlations, including mass enhancement [10], were observed in narrow, metallic SrTiO 3 quantum wells bound by two such interfaces. This is remarkable because bulk SrTiO 3 is a band insulator with cubic symmetry.…”

Quasiparticle mass enhancement and Fermi surface shape modification in oxide two-dimensional electron gases

“…To date the most common quantum well material is SrTiO 3 and the number of delectrons per metal in the quantum wells is typically, although not always 8,9 , much less than one. Oxide twodimensional electron systems have application potential because, as in the case of covalent semiconductors, large relative changes in the quantum well carrier density can be achieved by electrical means.…”