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 Kand Pd L3-edge x-ray absorption results show that the density of states, N(E), near the Fermi level, EF , jumps to a larger value when r decreases down to below about 20.6. The valence-band PES results show that N(E) near EF 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 EF for r58.3 QC, while it decreases smoothly down to zero at EF for larger r’s. The combined results suggest the occurrence of metal–insulator transition at an r between 13 and 20.6. © 2003 American Institute of Physics. @DOI: 10.1063/1.1565183#