We measured polarized far-infrared reflectivity and Raman scattering spectra of SrCuO2 single crystals. The frequencies for infrared-active modes were determined using an oscillator-fitting procedure of reflectivity data. The Raman spectra were measured at different temperatures using several laser energies ωL. In addition to eight of twelve Raman active modes, predicted by factor-group analysis, we observed a complex structure in the Raman spectra for polarization parallel to the {\bf c}-axis, which consists of Raman-allowed Ag symmetry modes, and B1u LO infrared-active (Raman-forbidden) modes of the first and higher order as well as their combinations. The Raman-forbidden modes have a stronger intensity at higher ωL than the Raman-allowed ones. In order to explain this resonance effect, we measured the dielectric function and optical reflection spectra of SrCuO2 in the visible range. We show that the Raman-allowed Ag symmetry modes are resonantly enhanced when a laser energy is close to E0, while Raman-forbidden (IR-active) modes resonate strongly for laser line energies close to the electronic transition of higher energy gaps.
@article{arxiv.cond-mat/0010221,
title = {Polarized far-infrared and Raman spectra of SrCuO2 single crystals},
author = {Z. V. Popović and M. J. Konstantinović and R. Gajić and C. Thomsen and U. Kuhlmann and A. Vietkin},
journal= {arXiv preprint arXiv:cond-mat/0010221},
year = {2009}
}