Valence fluctuation in Yb3Si5 probed by synchrotron x-ray photoemission spectroscopy


 We report the direct evidence of valence fluctuation in thermoelectric material Yb3Si5 by using synchrotron x-ray photoemission spectroscopy. Yb 3d core level photoemission spectrum of Yb3Si5 single crystal shows clear separation of Yb2+ peak and Yb3+ multiplet peaks. From the spectral weight of each component, the mean valence of Yb ions is estimated to be +2.67 at 20 K. Furthermore, Kondo resonance peak just below the Fermi energy is also observed by high resolution soft x-ray photoemission spectroscopy, suggesting the valence fluctuating state in Yb3Si5.