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

Abstract

Valence-band electronic structure of YbXCu4 (X = In, Cd, Mg) has been investigated by means of high-energy-resolution photoemission spectroscopy with an He I resonance line (hν = 21.22 eV) from 10 to 300 K. In the photoemission spectra of YbInCu4 and YbCdCu4 near the Fermi level (EF) measured at 10 K, the prominent peak structures due to the Yb2+ 4f7/2 states are clearly observed at 46 and 31 meV, respectively. The difference of the peak energies qualitatively reflects that of the Kondo temperatures between YbInCu4 and YbCdCu4. The peak intensities increase gradually with decreasing temperature for both compounds. The amount of enhancement of the Yb2+ 4f7/2 peak from 50 to 10 K is, however, much stronger for YbInCu4 than for YbCdCu4, due to an increase of the Yb2+ component followed by the valence transition at Tv = 42 K in YbInCu4. On the other hand, the Yb2+ 4f7/2 states of YbMgCu4 is observed as a broad structure near EF in the photoemission spectrum at 10 K. We have also measured the x-ray photoemission spectra in the Yb 4d core state region of YbXCu4 from 10 to 300 K. For YbInCu4 and YbCdCu4, the structures due to the Yb2+ and Yb3+ components are recognized for all temperatures. In particular, the Yb2+ structure is still observed at 300 K for YbInCu4. The intensity ratio of Yb2+/Yb3+ increases gradually with decreasing temperature for both compounds. For YbMgCu4, on the other hand, almost only Yb2+ structures are observed and little temperature dependence is detected.