Tunneling Density of States in Quasicrystals and Approximants

Using a low temperature Scanning Tunneling Microscope and a break-junction tunneling technique, the tunneling density of states (DOS) measurements on oxidized and bare surfaces of quasicrystalline icosahedral i-AlPdRe and i-AlCuFe, and of the approximant α-AlMnSi, as well as crystalline non-approximant ω-AlCuFe phase were performed. A narrow pseudogap at the Fermi level of about 50 meV width was found in tunneling spectra of icosahedral and approximant phases. For higher energies, the DOS exhibits a square root energy dependence attributed to electron–electron interaction effects. The tunneling DOS differs from the LMTO calculated DOS. The possible role of the electron scattering and the non-homogeneous electronic structure close to the surface are discussed.