Polarization Dependent Bulk-sensitive Valence Band Photoemission Spectroscopy and Density Functional Theory Calculations: Part II. 4d Transition Metals

Bulk-sensitive X-ray polarization dependent valence band photoelectron spectra of the 4d transition metals (TMs) of Y, Zr, Nb, Mo, Ru, Rh, Pd, and Ag were measured with hard X-ray photoelectron spectroscopy (HAXPES). The valence band spectral shapes of 4d TMs were modified by the X-ray polarization, but the changes of the spectral shapes of the 44 TMs were smaller than those of the 3d TMs [S. Ueda and I. Hamada, J. Phys. Soc. Jpn. 86, 124706 (2017)]. We simulated the HAXPES spectra, which correspond to the cross-section weighted densities of states (DOSs), where the 4d, 5s, and 5p partial DOSs were obtained by the density functional theory calculations. By comparing the polarization dependent experimental and simulated IIAXPES spectra, the relative photoionization cross-sections of the 5s and 5p orbitals to the 4d orbital were determined. The simulated IIAXPES spectra reproduced well the tendency of the experimental spectra for the 4d TMs, in contrast to the case of 3d TMs, in which the 3d 3d electron correlation plays an important role in the electronic structures. This result indicates that the 4d states are delocalized and the electron correlation is very weak in the 4d TMs.