Abstract
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.
Highlights
Since the discovery of a variety of interfacial electronic states between insulating and non-magnetic (001)-oriented LaAlO3 and SrTiO3, such as high-mobility metallic states[1], superconductivity[2, 3], and magnetism[4,5,6,7], the origin of these properties has been widely discussed[8, 9]
Depth resolution was achieved by varying the energy of the synchrotron-radiation light source - both soft x-ray photoemission spectroscopy (PES) (SX-PES) and hard x-ray PES (HAX-PES) were utilized - combined with precise tuning of the incident and emission angles[24]
In order to compare the experimentally obtained spectra with our model, we introduce an evaluation function known as the core-level intensity spectrum I(E)
Summary
Since the discovery of a variety of interfacial electronic states between insulating and non-magnetic (001)-oriented LaAlO3 and SrTiO3, such as high-mobility metallic states[1], superconductivity[2, 3], and magnetism[4,5,6,7], the origin of these properties has been widely discussed[8, 9]. An in situ photoemission spectroscopy (PES) study revealed downward band bending toward the interface in the SrTiO317 Notable in this system is the dramatic tunability of the interfacial conductivity using external electric fields, attracting considerable attention for fundamental studies, as well as device applications[18, 19]. Analysis of the SX-PES and HAX-PES core-level spectra with negative Vg reveal an abrupt downward shift of the potential, narrowing the electron confinement to within ~2 nm of the LaAlO3/SrTiO3 interface. These results explain why back-gate depletion modulates the mobility far more strongly than the carrier density, and suggests this is a generic feature of nonlinear dielectrics that can be utilized in device structures
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