  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 tells us that the
linear dichroism reflects the anisotropic charge distributions resulting from
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 low temperature well below the first excitation energy.
The excited-state symmetry is also probed by temperature dependence of the
linear dichroism where the high measuring temperatures are of the order of the
crystal-field-splitting energies.
