Valence band structure of the icosahedral Ag-In-Yb quasicrystal

Abstract

The valence band structure of the icosahedral $(i)$ Ag-In-Yb quasicrystal, which is isostructural to the binary $i\text{-Cd-Yb}$ system, is investigated by ultraviolet photoemission spectroscopy (UPS). Experimental results are compared with electronic-structure calculations of a cubic approximant of the same phase. UPS spectra from the fivefold, threefold, and twofold $i\text{-Ag-In-Yb}$ surfaces reveal that the valence band near to the Fermi level is dominated by $\text{Yb}\text{ }4f$-derived states, in agreement with calculations. The spectra also exhibit peaks which are surface core level shifted, caused by changes in the electronic structure in surface layers. Calculations yield a pseudogap in the density of states due to a hybridization of the $\text{Yb}\text{ }5d$ band with the $\text{Ag}\text{ }5p$ and $\text{In}\text{ }5p$ bands. Both experimental and calculated band features are very similar to those of Cd-Yb. The modification of the band structure after surface treatment by sputtering and by oxidation is also studied. Additionally, the work function of $i\text{-Ag-In-Yb}$ measured from the width of UPS spectrum is found to be almost unaffected by surface orientation, but increases after sputtering or oxidation.