We investigate the optical conductivity of Sr1−xCaxRuO3 across the ferromagnetic to paramagnetic transition that occurs at x=0.8. The thin films were grown by metalorganic aerosol deposition with 0≤x≤1 onto NdGaO3 substrates. We performed THz frequency domain spectroscopy in a frequency range from 3~cm−1 to 40~cm−1 (100~GHz to 1.4~THz) and at temperatures ranging from 5~K to 300~K, measuring transmittivity and phase shift through the films. From this we obtained real and imaginary parts of the optical conductivity. The end-members, ferromagnetic SrRuO3 and paramagnetic CaRuO3, show a strongly frequency-dependent metallic response at temperatures below 20~K. Due to the high quality of these samples we can access pronounced intrinsic electronic contributions to the optical scattering rate, which at 1.4~THz exceeds the residual scattering rate by more than a factor of three. Deviations from a Drude response start at about 0.7~THz for both end-members in a remarkably similar way. For the intermediate members a higher residual scattering originating in the compositional disorder leads to a featureless optical response, instead. The relevance of low-lying interband transitions is addressed by a calculation of the optical conductivity within density functional theory in the local density approximation (LDA).
@article{arxiv.1601.08236,
title = {THz conductivity of Sr$_{1-x}$Ca$_x$RuO$_3$},
author = {Diana Geiger and Uwe S. Pracht and Martin Dressel and Jernej Mravlje and Melanie Schneider and Philipp Gegenwart and Marc Scheffler},
journal= {arXiv preprint arXiv:1601.08236},
year = {2016}
}