Christopher J Winta, Sandy Gewinner, Wieland Schöllkopf, Martin Wolf, and Alexander Paarmann:
Phys. Rev. B 97 (9), 094108 (2018), pp.11;
arXiv:1710.02097 [cond-mat.mtrl-sci] (2017), pp. 12;
DOI: arXiv:1710.02097 [cond-mat.mtrl-sci]
We demonstrate midinfrared second-harmonic generation as a highly sensitive phonon spectroscopy technique that we exemplify using α-quartz (SiO2) as a model system. A midinfrared free-electron laser provides direct access to optical phonon resonances ranging from 350 to 1400 cm-1. While the extremely wide tunability and high peak fields of a free-electron laser promote nonlinear spectroscopic studies-complemented by simultaneous linear reflectivity measurements-azimuthal scans reveal crystallographic symmetry information of the sample. Additionally, temperature-dependent measurements show how damping rates increase, phonon modes shift spectrally and in certain cases disappear completely when approaching Tc=846K where quartz undergoes a structural phase transition from trigonal a-quartz to hexagonal β-quartz, demonstrating the technique's potential for studies of phase transitions.
The original publication is available by link DOI: 10.1103/PhysRevB.97.094108