Berlin 2018 – wissenschaftliches Programm
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 1: Whispering Gallery Mode Resonators I
KFM 1.6: Vortrag
Montag, 12. März 2018, 11:50–12:10, EMH 025
Phase transition studies using second-harmonic phonon spectroscopy — •Christopher J. Winta, Sandy Gewinner, Wieland Schöllkopf, Martin Wolf, and Alexander Paarmann — Fritz-Haber-Institut der MPG
Nonlinear optical spectroscopy constitutes a powerful tool for the investigation of crystalline solids and their structure. Apart from improved sensitivity compared to linear techniques, it offers additional experimental degrees of freedom which can be used to selectively study different symmetry components of the detected signal. The mid-infrared (MIR) spectral region is particularly interesting as it contains optical phonon resonances which themselves carry symmetry information.
Here, we demonstrate MIR second-harmonic (SH) phonon spectroscopy [1] as a symmetry-sensitive technique to investigate structural phase transitions, using the α→β transition of quartz as a case example. A MIR free-electron laser grants access to essentially all optical phonon resonances of quartz which are selectively investigated with regard to their temperature-dependent behavior upon Tc. The data show a critical phase transition behavior of the phonon frequencies, damping rates and SH peak amplitudes. Additionally, certain phonon modes become IR-forbidden in the higher symmetry β-phase and consequently disappear from the SH spectra upon the phase transition.
Given its sensitivity to crystal structure and symmetry, our novel technique presents itself as a promising tool for the study of structural phase transitions in polar dielectrics, e.g. ferroelectrics or multiferroics.
Winta et al., arXiv:1710.02097 (2017)