Dielectric collapse at the LaAlO₃/SrTiO₃ (001) heterointerface under applied electric field

The fascinating interfacial transport properties at the LaAlO₃/SrTiO₃ heterointerface have led to intense investigations of this oxide system. Exploiting the large dielectric constant of SrTiO₃ at low temperatures, tunability in the interfacial conductivity over a wide range has been demonstrated using a back-gate device geometry. In order to understand the effect of back-gating, it is crucial to assess the interface band structure and its evolution with external bias. In this study, we report measurements of the gate-bias dependent interface band alignment, especially the confining potential profile, at the conducting LaAlO₃/SrTiO₃ (001) heterointerface using soft and hard x-ray photoemission spectroscopy in conjunction with detailed model simulations. Depth-profiling analysis incorporating the electric field dependent dielectric constant in SrTiO₃ reveals that a significant potential drop on the SrTiO₃ side of the interface occurs within ~2 nm of the interface under negative gate-bias. These results demonstrate gate control of the collapse of the dielectric permittivity at the interface, and explain the dramatic loss of electron mobility with back-gate depletion.