Ultraviolet Photoemission Studies of Highly Correlated Electron Systems in Sm, Yb and U Pnictides

Abstract

Ultraviolet photoemission spectra have been measured for single crystals of Sm4As3, Sm4Bi3, Yb4Sb3, Yb4Bi3, U3P4 and U3As4 by use of synchrotron radiation. Constant initial state (CIS) and constant final state (CFS) spectra have been measured as well. The complicated electronic structures are elucidated by considering the p-f mixing and Coulomb-exchange interactions.Sm4As3 is a predominantly trivalent material, which shows the Kondo behaviour. The spectral shape near the Fermi level (EF) has shown a drastic hv dependence below 60 eV. The structure at EB (binding energy from EF) = 1.0 eV is found to be dominated by the Sm2+ 4f states, for which the p-f mixing effect is essential and provides the valence fluctuation (VF). The sharp structure intersecting EF is assigned to the Sm 5d conduction band states. Sm4Bi3 has shown the mixed valence, whereas the density of divalent Sm states is small at EF. The effective correlation energy U(4f, 4f) is evaluated as 5.6 eV.Yb4Sb3 and Yb4Bi3 have also shown the VF, with appreciable density of states (DOS) of the divalent Yb4f states as well as of the anion p states at EF. The contribution of the surface 4f states is resolved. The upper limit of the mean valence is evaluated as 2.36 and 2.37 for Yb4Sb3 and Yb4Bi3.In the cases of U3P4 and U3As4, the 5f features are observed around EB = 0.7-0.8 and 1.9-2.0 eV reflecting the strong p-f mixing effect, whereas the 6d states are observed closer to EF. The 5f states are partly mixed with 6d band, providing the VF. Many Auger structures are resolved in both materials, from which U(5f, 5f) is evaluated as 1.2 eV.