Two-dimensional electron gas at the LaAlO3/SrTiO3 inteface with a potential barrier

Abstract

We present a tight binding description of electronic properties of the interface between LaAlO₃ (LAO) and SrTiO₃ (STO). The description assumes LAO and STO perovskites as sets of atomic layers in the x–y plane, which are weakly coupled by an interlayer hopping term along the z axis. The interface is described by an additional potential, U₀, which simulates a planar defect. Physically, the interfacial potential can result from either a mechanical stress at the interface or other structural imperfections. We show that depending on the potential strength, charge carriers (electrons or holes) may form an energy band which is localized at the interface and is within the band gaps of the constitutent materials (LAO and STO). Moreover, our description predicts a valve effect at a certain critical potential strength, U_0cr, when the interface potential works as a valve suppressing the interfacial conductivity. In other words, the interfacial electrons become dispersionless at U₀ = U_0cr, and thus cannot propagate. This critical value separates the quasielectron (U₀ < U_0cr) and quasihole (U₀ > U_0cr) regimes of the interfacial conductivity.