Unusual line shape of B 1s core level spectra in rare earth hexaborides

We investigate the B 1s core level spectra of hexaborides, R B 6 ( R = La , Ce, Pr, Nd), using high resolution X-ray photoemission spectroscopy. While all the B sites are identical, the experimental spectra exhibit a signature of multiple features manifested as an unusual asymmetry in the lower binding energy side. The analysis of the spectra reveals that the surface and bulk photoemission signals are different. In addition, the peak position shifts towards lower binding energies with the increase in 4f binding energy of the rare earth elements that can be attributed to the chemical potential shift due to lower degree of 4f–conduction electron hybridization. Decrease in temperature leads to a narrowing of the linewidth in every case. The Kondo systems exhibit more prominent narrowing of the B 1s linewidth.