  Two-dimensional (2D) perovskite oxide interfaces are ideal systems where
diverse emergent properties can be uncovered.The formation and modification of
polaronic properties due to short-range strong charge-lattice interactions of
2D interfaces remains hugely intriguing.Here, we report the direct observation
of small-polarons at the LaAlO3/SrTiO3 (LAO/STO) conducting interface using
high-resolution spectroscopic ellipsometry.First-principles investigations
further reveals that strong coupling between the interfacial electrons and the
Ti-lattice result in the formation of localized 2D small polarons.These
findings resolve the longstanding issue where the excess experimentally
measured interfacial carrier density is significantly lower than theoretically
predicted values.The charge-phonon induced lattice distortion further provides
an analogue to the superconductive states in magic-angle twisted bilayer
graphene attributed to the many-body correlations induced by broken periodic
lattice symmetry.Our study sheds light on the multifaceted complexity of broken
periodic lattice induced quasi-particle effects and its relationship with
superconductivity.
