Enhanced surface metallic density of states in icosahedral quasicrystals

Abstract

Valence and core-level photoemission spectra show that cleaved i-Al-Pd-Mn quasicrystals have a pronounced metallic signature. Spectra from states above E_F, populated by increasing the sample temperature, indicate the presence of a shallow pseudogap 0.09 eV above E_F. The Al 2p line asymmetry, on the other hand, which indicates metallic behavior, decreases with increasing photoelectron escape depth. This implies a decreasing density of states at E_F with increasing distance from the surface, 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 pseudogap, and the clear metallic Fermi edges in photoemission.