Low-temperature scanning tunneling spectroscopy on the 5-fold surface of the icosahedral AlPdMn quasicrystal

摘要

We report on scanning tunneling spectroscopy investigations at low temperature (5.3 K) on a bare 5-fold surface of an icosahedral Al70Pd21Mn9 quasicrystal. By averaging tunneling spectra recorded over several nm(2) we could reproduce the typical line shape observed in point contact spectroscopy on oxidized surfaces. The averaged spectra show a large parabolic gap structure with a sharp dip of 20 meV FWHM at the Fermi energy. Whereas the averaged spectrum is relatively smooth and featureless, with exception of the sharp dip structure, the individual spectra show a rich structure of peaks and gaps. The distribution of the peak positions in energy shows a clear asymmetry between the occupied and the unoccupied states, in the sense that the peaks are mainly situated above the Fermi energy. The FWHM of these peaks is typically between 30 meV and 100 meV. The spectral features vary rapidly with tip position, where the spatial extent of a given peak in the spectrum is of the order of 0.5-1 nm. To the best of our knowledge, we will present for the first time LT-STS data in combination with high resolution STM images of a quasicrystalline surface to demonstrate the localization of electronic states and gaps and the asymmetry between the occupied and the unoccupied local density of states.