Electronic structure of YbXCu(4) (X = In, Cd, Mg) investigated by high-resolution photoemission spectroscopy

The valence-band electronic structure of YbXCu(4) (X = In, Cd, Mg) has been investigated by means of temperature-dependent high-energy-resolution photoemission spectroscopy using a He I resonance line (hnu = 21.22 eV) and synchrotron radiation (hnu = 800 eV). Intensities of the structure due to the Yb(2+) 4f(7/2) states in the He I spectra of YbInCu(4) and YbCdCu(4) gradually increase with decreasing temperature from 300 to 10 K, and Yb(2+) 4f(7/2) structures are clearly observed as peaks near the Fermi level (E(F)) at 10 K. The enhancement of the Yb(2+) 4f(7/2) peak from 50 to 10 K is much greater for YbInCu(4) than for YbCdCu(4). On the other hand, the Yb(2+) 4f(7/2) states of YbMgCu(4) are observed as a broad structure near E(F). In the synchrotron radiation photoemission spectra of YbInCu(4) and YbCdCu(4), the structures due to the Yb(2+) and Yb(3+) 4f states are recognized at all temperatures. The intensity ratio Yb(2+)/Yb(3+) gradually increases with decreasing temperature. The energy separations between the Yb(2+) and Yb(3+) 4f structures of YbInCu(4) increase from 50 to 20 K. For YbMgCu(4), on the other hand, almost only the Yb(2+) structures are observed and little temperature dependence has been detected.