Dynamical Response and Confinement of the Electrons at the LaAlO3/SrTiO3 Interface

With infrared ellipsometry and transport measurements we investigated the electrons at the interface between LaAlO₃ and SrTiO₃. We obtained a sheet carrier concentration of N_s≈5-9×10¹³cm^-2, an effective mass of m^*=3.2±0.4m_e, and a strongly frequency dependent mobility. The latter are similar as in bulk SrTi_1-xNb_xO₃ and therefore suggestive of polaronic correlations. We also determined the vertical concentration profile which has a strongly asymmetric shape with a rapid initial decay over the first 2 nm and a pronounced tail that extends to about 11 nm.