Observation of metal-insulator transition in Al-Pd-Re quasicrystals by x-ray absorption and photoemission spectroscopy

Using x-ray absorption and valence-band photoelectron spectroscopy (PES) we investigated the electronic structures of icosahedral (i)-Al70Pd22.5Re7.5 quasicrystals (QCs) with a 4.2 K/300 K resistivity ratio, r, ranging from 8.3 to 107 obtained under various annealing conditions. Our Al K- and Pd L-3-edge x-ray absorption results show that the density of states, N(E), near the Fermi level, E-F, jumps to a larger value when r decreases down to below about 20.6. The valence-band PES results show that N(E) near E-F is greatly reduced in i-Al70Pd22.5Re7.5 QCs relative to that of the pure metal, which confirms the existence of the pseudogap. The PES spectrum has a sharp cutoff at E-F for r=8.3 QC, while it decreases smoothly down to zero at E-F for larger r's. The combined results suggest the occurrence of metal-insulator transition at an r between 13 and 20.6. (C) 2003 American Institute of Physics.