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arXiv · 2203.13651

Spin-orbit coupling and crystal-field splitting in Ti-doped Ca2RuO4 studied by ellipsometry

I. Vergara·M. Magnaterra·J. Attig·S. Kunkemöller·D. I. Khomskii·M. Braden·M. Hermanns·M. Grüninger
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Abstract

In Ca2RuO4, the competition of spin-orbit coupling $\zeta$ and tetragonal crystal field splitting $\Delta_{CF}$ has been discussed controversially for many years. The orbital occupation depends on $\Delta_{CF}/\zeta$, which allows us to address this ratio via the optical spectral weights of the lowest intersite Mott-Hubbard excitations. We study the optical conductivity of Ca$_2$Ru$_{0.99}$Ti$_{0.01}$O$_4$ in the range of 0.75 - 5 eV by ellipsometry, using the large single crystals that can be grown for small Ti concentrations. Based on a local multiplet calculation, our analysis results in $2.4 \leq \Delta_{CF}/\zeta \leq 4$ at 15 K. The dominant crystal field yields a ground state close to xy orbital order but spin-orbit coupling is essential for a quantitative description of the properties. Furthermore, we observe a pronounced decrease of $\Delta_{CF}$ with increasing temperature, as expected based on the reduction of octahedral distortions.

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I. Vergara, M. Magnaterra, J. Attig, S. Kunkemöller, D. I. Khomskii, M. Braden, M. Hermanns, M. Grüninger. 2022-03-25. Spin-orbit coupling and crystal-field splitting in Ti-doped Ca2RuO4 studied by ellipsometry. https://doi.org/10.1103/physrevb.106.085103

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