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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 14: Poster

KFM 14.10: Poster

Mittwoch, 19. März 2025, 17:00–18:30, P1

Nanoscale Thermal Expansion in Crystals Probed by Echo-Resolved Terahertz Spectroscopy — •Nicolas Sylvester Beermann, Andreas Gebauer, Wentao Zhang, Tomoki Hiraoka, Savio Fabretti, Hassan Hafez, and Dmitry Turchinovich — Fakultät für Physik, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld, Germany

Thermal expansion of solids is a ubiquitous phenomenon in condensed matter physics [1]. However, its observation was out of limits for terahertz time-domain spectroscopy (THz-TDS) due to the relatively long sub-millimeter wavelength of THz radiation. To address this, we introduce echo-resolved THz spectroscopy (ERTS) that utilizes THz main and echo pulses in time-domain measurements to simultaneously determine frequency-dependent complex optical constants and material thickness [2]. By numerically solving complex transcendental transmission equations, ERTS allows for sample thickness measurements with deep-subwavelength precision on the order of λ/1000. We used the ERTS to analyze the THz-TDS data of magnesium oxide, sapphire, and gallium arsenide crystals measured in the temperature range of 10-300 K. The thermal expansion of the crystals on a sub-micrometer scale was measured, and the simple phonon model was applied to determine the material-specific Grüneisen parameters.

[1] K. Takenaka, Sci. Technol. Adv. Mater. 13, 13001 (2012)

[2] N. S. Beermann et al., Terahertz Time-Domain Spectroscopy for Simultaneous Measurement of Optical Constants, and Material Thickness with Deep-Subwavelength Precision, submitted manuscript

Keywords: Terahertz spectroscopy; Echo-resolved THz spectroscopy; Thermal expansion; Dielectric constants; Crystals