THz conductivity of Sr${}_{1-x}$Ca${}_x$RuO${}_3$

Abstract

We investigate the optical conductivity of Sr${}_{1-x}$Ca${}_x$RuO${}_3$ across the ferromagnetic to paramagnetic transition that occurs at $x=0.8$. The thin films were grown by metalorganic aerosol deposition with $0\le x\le 1$ onto NdGaO${}_3$ 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 SrRuO${}_3$ and paramagnetic CaRuO${}_3$, 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).

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Cited by in corpus (6)

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• Revealing the Hidden Heavy Fermi Liquid in CaRuO3
• Superconducting coplanar microwave resonators with operating frequencies up to 50 GHz
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• Can disorder act as a chemical pressure? An optical study of the Hubbard model