Revealing the Interaction of Charge Carrier–Phonon Coupling by Quantification of Electronic Properties at the SrTiO3/TiO2 Heterointerface

T.-X. Qin, E.-M. You, J.-Y. Zhang, H.-L. Wang, K. H. L. Zhang, B.-W. Mao, Z.-Q. Tian

Nano Letters, 2022, 22, 2755 (2022)
Oxide heterointerfaces with high carrier density can interact strongly with the lattice phonons, generating considerable plasmon–phonon coupling and thereby perturbing the fascinating optical and electronic properties, such as two-dimensional electron gas, ferromagnetism, and superconductivity. Here we use infrared-spectroscopic nanoimaging based on scattering-type scanning near-field optical microscopy (s-SNOM) to quantify the interaction of electron–phonon coupling and the spatial distribution of local charge carriers at the SrTiO3/TiO2 interface. We found an increased high-frequency dielectric constant (ε∞ = 7.1–9.0) and charge carrier density (n = 6.5 × 1019 to 1.5 × 1020 cm–3) near the heterointerface. Moreover, quantitative information between the charge carrier density and extension thickness across the heterointerface has been extracted by monochromatic near-field imaging. A direct evaluation of the relationship between the thickness and the interaction of charge carrier–phonon coupling of the heterointerface would provide valuable information for the development of oxide-based electronic devices.