Towards Two-Dimensional Metallic Behavior at LaAlO3/SrTiO3 Interfaces

Using a low-temperature conductive-tip atomic force microscope in cross-section geometry we have characterized the local transport properties of the metallic electron gas that forms at the interface between LaAlO₃ and SrTiO₃. At low temperature, we find that the carriers do not spread away from the interface but are confined within ∼10nm, just like at room temperature. Simulations taking into account both the large temperature and electric-field dependence of the permittivity of SrTiO₃ predict a confinement over a few nm for sheet carrier densities larger than ∼6×10¹³cm^-2. We discuss the experimental and simulations results in terms of a multiband carrier system. Remarkably, the Fermi wavelength estimated from Hall measurements is ∼16nm, indicating that the electron gas in on the verge of two dimensionality.