  The highly mobile electrons at the interface of SrTiO3 with other oxide
insulators, such as LaAlO3 or AlOx, are of great current interest. A vertical
gate voltage allows controlling a metal/superconductor-to-insulator transition,
as well as electrical modulation of the spin-orbit Rashba coupling for
spin-charge conversion. These findings raise important questions about the
origin of the confined electrons as well as the mechanisms that govern the
interfacial electric field. Here we use infrared ellipsometry and confocal
Raman spectroscopy to show that an anomalous polar moment is induced at the
interface that is non-collinear, highly asymmetric and hysteretic with respect
to the vertical gate electric field. Our data indicate that an important role
is played by the electromigration of oxygen vacancies and their clustering at
the antiferrodistortive domain boundaries of SrTiO3, which generates local
electric and possibly also flexoelectric fields and subsequent polar moments
with a large lateral component. Our results open new perspectives for the
defect engineering of lateral devices with strongly enhanced and hysteretic
local electric fields that can be manipulated with various other parameters,
like strain, temperature, or photons.
