Phonon-enhanced infrared near-field spectroscopy enables probing of the buried 2DEG at the LAO/STO interface

The interface between bulk insulators SrTiO3 and LaAlO3 (LAO/STO) gives rise to a confined and highly conductive two-dimensional electron gas (2DEG) [1], which poses unique analytical challenges, due to its buried and sensitive nature. Scanning near-field optical microscopy (SNOM) was shown to detect the electronic properties of the LAO/STO 2DEG using highly confined optical near-fields. Here, we used our models to compare different vertical distributions of the interfacial free charge carriers and explore the resulting coupled plasmon-phonon polariton modes. Finally, we predict a transition from phonon-dominated to electron-dominated response at higher mobilities, which should be achievable in low-temperature SNOM measurements.