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News 13.02.2024
New publication: An open-source robust machine learning platform for real-time detection and classification of 2D material flakes

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News 24.10.2022

New publication: The Reststrahlen Effect in the Optically Thin Limit: A Framework for Resonant Response in Thin Media

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Nano Letters 22, 8389 (2022)
Sharp resonances can strongly modify the electromagnetic response of matter. A classic example is the Reststrahlen effect – high reflectivity in the mid-infrared in many polar crystals near their optical phonon resonances. Although this effect in bulk materials has been studied extensively, a systematic treatment for finite thickness remains challenging. Here we describe, experimentally and theoretically, the Reststrahlen response in hexagonal boron nitride across more than 5 orders of magnitude in thickness, down to a monolayer. We find that the high reflectivity plateau of the Reststrahlen band evolves into a single peak as the material enters the optically thin limit, within which two distinct regimes emerge: a strong-response regime dominated by coherent radiative decay and a weak-response regime dominated by damping. We show that this evolution can be explained by a simple two-dimensional sheet model that can be applied to a wide range of thin media.

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