A. Severing

Determining the crystal-field ground state in rare earth heavy fermion materials using soft-x-ray absorption spectroscopy.

We infer that soft-x-ray absorption spectroscopy is a versatile method for the determination of the crystal-field ground state symmetry of rare earth heavy fermion systems, complementing neutron scattering. Using realistic and universal parameters, we provide a theoretical mapping between the polarization dependence of Ce M(4,5) spectra and the charge distribution of the Ce 4f states. The experimental resolution can be orders of magnitude larger than the 4f crystal-field splitting itself. To demonstrate the experimental feasibility of the method, we investigated CePd2Si2, thereby settling an existing disagreement about its crystal-field ground state.

Crystal-field ground state of the orthorhombic Kondo insulator CeRu2Al10

We have succeeded in establishing the crystal-field ground state of CeRu2Al10, an orthorhombic intermetallic compound recently identified as a Kondo insulator. Using polarization dependent soft x-ray absorption spectroscopy at the Ce M4,5 edges, together with input from inelastic neutron and magnetic susceptibility experiments, we were able to determine unambiguously the orbital occupation of the 4f shell and to explain quantitatively both the measured magnetic moment along the easy a axis and the small ordered moment along the c-axis. The results provide not only a platform for a realistic modeling of the spin and charge gap of CeRu2Al10, but demonstrate also the potential of soft x-ray absorption spectroscopy to obtain information not easily accessible by neutron techniques for the study of Kondo insulators in general.

Determining the In-Plane Orientation of the Ground-State Orbital of CeCu2Si2

We have successfully determined the hitherto unknown sign of the B(4)(4) Stevens crystal-field parameter of the tetragonal heavy-fermion compound CeCu(2)Si(2) using vector q-dependent nonresonant inelastic x-ray scattering experiments at the cerium N(4,5) edge. The observed difference between the two different directions, q∥[100] and q∥[110], is due to the anisotropy of the crystal-field ground state in the (001) plane and is observable only because of the utilization of higher than dipole transitions possible in nonresonant inelastic x-ray scattering. This approach allows us to go beyond the specific limitations of dc magnetic susceptibility, inelastic neutron scattering, and soft x-ray spectroscopy, and provides us with a reliable information about the orbital state of the 4f electrons relevant for the quantitative modeling of the quasiparticles and their interactions in heavy-fermion systems.

4f Crystal Field Ground State of the Strongly Correlated Topological Insulator SmB6

We investigated the crystal-electric field ground state of the 4f manifold in the strongly correlated topological insulator SmB_{6} using core-level nonresonant inelastic x-ray scattering. The directional dependence of the scattering function that arises from higher multipole transitions establishes unambiguously that the Γ_{8} quartet state of the Sm f^{5}u2009u2009J=5/2 configuration governs the ground-state symmetry and, hence, the topological properties of SmB_{6}. Our findings contradict the results of density functional calculations reported so far.

Evolution of ground-state wave function in CeCoIn5 upon Cd or Sn doping

We present linear polarization-dependent soft x-ray absorption spectroscopy data at the Ce

Neutron scattering experiments on Yb X Cu sub 4 and Er X Cu sub 4 ( X =Au, Pd, and Ag)

M_{4,5}

GAP IN THE MAGNETIC EXCITATION SPECTRUM OF CE3BI4PT3

edges of Cd and Sn doped CeCoIn

Spectroscopic determination of crystal-field levels in CeRh2Si2 and CeRu2Si2 and of the 4f0 contributions in CeM2Si2 (M=Cu, Ru, Rh, Pd, and Au)

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Crystal field ground state of the orthorhombic Kondo semiconductors CeOs2Al10 and CeFe2Al10

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Absence of orbital rotation in superconducting CeCu2Ge2

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