Possible multi-orbital ground state in CeCu${}_2$Si${}_2$

Abstract

The crystal-field ground state wave function of CeCu${}_2$Si${}_2$ has been investigated with linear polarized $M$-edge x-ray absorption spectroscopy from 250mK to 250K, thus covering the superconducting ($T_{\text{c}}$=0.6K), the Kondo ($T_{\text{K}}$$\approx$20K) as well as the Curie-Weiss regime. The comparison with full-multiplet calculations shows that the temperature dependence of the experimental linear dichroism is well explained with a ${\Gamma }_7^{(1)}$ crystal-field ground-state and the thermal population of excited states at around 30meV. The crystal-field scheme does not change throughout the entire temperature range thus making the scenario of orbital switching unlikely. Spectroscopic evidence for the presence of the Ce 4$f^0$ configuration in the ground state is consistent with the possibility for a multi-orbital character of the ground state. We estimate from the Kondo temperature and crystal-field splitting energies that several percents of the higher lying ${\Gamma }_6$ state and ${\Gamma }_7^{(2)}$ crystal-field states are mixed into the primarily ${\Gamma }_7^{(1)}$ ground state. This estimate is also supported by re-normalized band-structure calculations that uses the experimentally determined crystal-field scheme.

8 pages, 5 figures

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• Spectroscopic evidence of Kondo-induced quasi-quartet in CeRh${}_2$As${}_2$
• Magnetic order and crystalline electric field excitations of the quantum critical heavy fermion ferromagnet CeRh${}_6$Ge${}_4$
• Orbital selective coupling in CeRh${}_3$B${}_2$: co-existence of high Curie and high Kondo temperature
• CeCu${}_2$Si${}_2$ and YbRh${}_2$Si${}_2$: Strange Cases of Heavy-Fermion Superconductivity
• Observation of field-induced single-ion magnetic anisotropy in a multiorbital Kondo alloy $(\mathrm{Lu},\mathrm{Yb}){\mathrm{Rh}}_2{\mathrm{Zn}}_{20}$
• The Kondo effect in ferromagnetic quantum critical CeRh${}_6$Ge${}_4$
• First-Principles Study of the Fermi Surface Topology of CeCu${}_2$Si${}_2$