Probing Strongly Correlated 4f-Orbital Symmetry of the Ground State in Yb Compounds by Linear Dichroism in Core-Level Photoemission

We show that the strongly correlated 4f-orbital symmetry of the ground state is revealed by linear dichroism in core-level photoemission spectra, as we have discovered for YbRh2Si2 and YbCu2Si2. Theoretical analysis shows us that the linear dichroism reflects the anisotropic charge distributions resulting from a crystalline electric field. We have successfully determined the ground-state 4f symmetry for both compounds from the polarization-dependent angle-resolved core-level spectra at a temperature well below the first excitation energy. The excited-state symmetry is also probed by temperature dependence of the linear dichroism where the high measurement temperatures are on the order of the crystal-field-splitting energies.