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.
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