Electronic Structure of Icosahedral Alloys Studied by Ultrahigh Energy Resolution Photoemission Spectroscopy

The results of a systematic ultrahigh resolution ultraviolet photoemission study of the electronic structure of stable icosahedral alloys ${\mathrm{Al}}_{64}$ ${\mathrm{Cu}}_{24}$ ${\mathrm{Fe}}_{12}$, ${\mathrm{Al}}_{65}$ ${\mathrm{Cu}}_{20}$ ${\mathrm{Fe}}_{15}$, ${\mathrm{Al}}_{70}$ ${\mathrm{Pd}}_{20}$ ${\mathrm{Mn}}_{10}$, and ${\mathrm{Al}}_{70.5}$ ${\mathrm{Pd}}_{21}$ ${\mathrm{Re}}_{8.5}$ are presented. It is shown that all icosahedral alloys have a clearly developed Fermi edge and are thus metallic down to the temperature of measurement (14-45 K). A marked decrease of the spectral intensity towards the Fermi level in these alloys is demonstrated to be consistent with the existence of the theoretically predicted pseudogap. With an experimental resolution of 6 meV, no evidence of the theoretically predicted spikiness of the density of states could be observed.