  We have successfully observed linear dichroism in angle-resolved Yb3+ 3d5/2
core-level photoemission spectra for YbB12 in cubic symmetry. Its anisotropic
4f charge distribution due to the crystal-field splitting is responsible for
the linear dichroism, which has been verified by spectral simulations using
ionic calculations with the full multiplet theory for a single-site Yb3+ ion in
cubic symmetry. The observed linear dichroism as well as the
polarization-dependent spectra in two different photoelectron directions for
YbB12 are quantitatively reproduced by theoretical analysis for the Gamma_8
ground state, indicating the Gamma_8 ground-state symmetry for the Yb3+ ions
mixed with the Yb2+ state.
