Electronic structure of YbXCu₄ (X = In, Cd, Mg) investigated by high-resolution photoemission spectroscopy

The valence-band electronic structure of YbXCu₄ (X = In, Cd, Mg) has been investigated by means of temperature-dependent high-energy-resolution photoemission spectroscopy using a He I resonance line (hν = 21.22 eV) and synchrotron radiation (hν = 800 eV). Intensities of the structure due to the Yb²⁺ 4f_7/2 states in the He I spectra of YbInCu₄ and YbCdCu₄ gradually increase with decreasing temperature from 300 to 10 K, and Yb²⁺ 4f_7/2 structures are clearly observed as peaks near the Fermi level (E_F) at 10 K. The enhancement of the Yb²⁺ 4f_7/2 peak from 50 to 10 K is much greater for YbInCu₄ than for YbCdCu₄. On the other hand, the Yb²⁺ 4f_7/2 states of YbMgCu₄ are observed as a broad structure near E_F. In the synchrotron radiation photoemission spectra of YbInCu₄ and YbCdCu₄, the structures due to the Yb²⁺ and Yb³⁺ 4f states are recognized at all temperatures. The intensity ratio Yb²⁺/Yb³⁺ gradually increases with decreasing temperature. The energy separations between the Yb²⁺ and Yb³⁺ 4f structures of YbInCu₄ increase from 50 to 20 K. For YbMgCu₄, on the other hand, almost only the Yb²⁺ structures are observed and little temperature dependence has been detected.