Electronic structure of quasicrystals studied by ultrahigh-energy-resolution photoemission spectroscopy

Abstract

The results of low-temperature, ultrahigh-resolution ultraviolet photoemission studies of the electronic structure of stable icosahedral ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{20}$${\mathrm{Fe}}_{15}$, ${\mathrm{Al}}_{64}$${\mathrm{Cu}}_{24}$${\mathrm{Fe}}_{12}$, ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{20}$${\mathrm{Ru}}_{15}$, ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{20}$${\mathrm{Ru}}_{7.5}$${\mathrm{Fe}}_{7.5}$, ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{20}$${\mathrm{Os}}_{15}$, ${\mathrm{Al}}_{70}$${\mathrm{Pd}}_{20}$${\mathrm{Mn}}_{10}$, ${\mathrm{Al}}_{70}$${\mathrm{Pd}}_{20}$${\mathrm{Cr}}_{5}$${\mathrm{Fe}}_{5}$, ${\mathrm{Al}}_{70.5}$${\mathrm{Pd}}_{21}$${\mathrm{Re}}_{8.5}$, and ${\mathrm{Zn}}_{60}$${\mathrm{Mg}}_{32}$${\mathrm{Y}}_{8}$, decagonal ${\mathrm{Al}}_{65}$${\mathrm{Co}}_{15}$${\mathrm{C}}_{20}$ and ${\mathrm{Al}}_{70}$${\mathrm{Co}}_{15}$${\mathrm{Ni}}_{15}$, and crystalline ${\mathrm{Al}}_{7}$${\mathrm{Cu}}_{2}$Ru and ${\mathrm{Ni}}_{2}$MnAl alloys are presented. It is shown that these alloys have a clearly developed Fermi edge, and are thus metallic down to the temperature of measurement (12--45 K). A marked decrease of the spectral intensity toward the Fermi level in quasicrystals is demonstrated to be consistent with the existence of the theoretically predicted pseudogap. With an experimental resolution of 5 meV, no evidence of the theoretically predicted spikiness of the density of states could be observed. A close similarity between the values and unusual dependencies of various physical parameters observed in quasicrystals and in their approximants suggests that they are not the consequence of the long-range quasiperiodicity, but rather result from a complex local atomic order. A review of the electronic properties of quasicrystals is also presented.