ENHANCED SURFACE METALLIC DENSITY-OF-STATES IN ICOSAHEDRAL QUASI-CRYSTALS

Valence and core-level photoemission spectra show that cleaved i-Al-Pd -Mn quasicrystals have a pronounced metallic signature. Spectra from s tates above E-F, populated by increasing the sample temperature, indic ate the presence of a shallow pseudogap 0.09 eV above E-F. The Al 2p l ine asymmetry, on the other hand, which indicates metallic behavior, d ecreases with increasing photoelectron escape depth. This implies a de creasing density of stales at E-F with increasing distance from the su rface, consistent with indications that the density of states near E-F in the bulk is reduced. Our results thus help to resolve the apparent contradiction between the theoretical predictions for a bulk pseudoga p, and the clear metallic Fermi edges in photoemission. [S0163-1829(98 )05726-9].