Revealing the Interaction of Charge Carrier-Phonon Coupling by Quantification of Electronic Properties at the SrTiO<sub>3</sub>/TiO<sub>2</sub> Heterointerface.

Qin, Ting-Xiao; You, En-Ming; Zhang, Jia-Ye; Wang, Hai-Long; Zhang, Kelvin H L; Mao, Bing-Wei; Tian, Zhong-Qun · Nano Lett · 2022

basic_science · Level V

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Abstract

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 SrTiO<sub>3</sub>/TiO<sub>2</sub> interface. We found an increased high-frequency dielectric constant (ε<sub>∞</sub> = 7.1-9.0) and charge carrier density (<i>n</i> = 6.5 × 10<sup>19</sup> to 1.5 × 10<sup>20</sup> cm<sup>-3</sup>) 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.