Electronic structure of quasicrystals studied by photoemission spectroscopy.

Abstract

To investigate the electronic structure of the high-quality quasicrystals, photoemission spectroscopy measurements have been carried out using synchrotron radiation source in the photo-energy range 35-150 eV. The studied quasicrystals are icosahedral Al$\rm\sb{70}Pd\sb{20}Mn\sb ,\ Al\sb{65}Cu\sb{20}Os\sb ,$ and $\rm Al\sb{65}Cu\sb{20}Ru\sb ,$ and decagonal $\rm Al\sb{65}Co\sb Cu\sb{20}$ and $\rm Al\sb{70}Co\sb Ni\sb .$ Resonance photoemission near the transition from the shallow core levels to the d valence bands has been employed to show that the feature close to the Fermi level in the valence bands is predominantly due to the d electron states in the nearly-half-full subshells (Mn, Fe, Ru, Os). The feature farther from the Fermi level has been identified as being mainly due to the d electron states in the full d subshells (Pd, Cu). In some cases, the experimental partial densities of states have been obtained by taking advantage of the synchrotron-radiation-based photoemission technique and the large changes in the cross sections. The as-measured valence-band spectra were corrected for the experimental parameters and the background in order to make a meaningful comparison between the spectra. The high energy-resolution ultraviolet photoelectron spectroscopy measurements on icosahedral $\rm Al\sb{65}Cu\sb{20}Fe\sb{7.5}Ru\sb{7.5}$ prove that there is a pseudogap from the d electrons close to the Fermi level. The studied samples were characterized by the X-ray diffraction and the diffraction patterns were indexed based on several indexing schemes. A description of the indexing procedures is presented. The experimental results of this work are related to the theoretical predictions of a pseudogap and spikiness in the density of states. The unusual behavior of the resistivity of the quasicrystals is interpreted in terms of disorder and other relevant theories.