Quasicrystals, materials with long-range order but no translational symmetry, provide a unique platform for studying unusual electronic properties. In particular, interference of electron waves in quasicrystals can lead to the emergence of fractal electronic spectra and localized states.
In this paper, we report the experimental observation of two-dimensional quantum interference effects in thin films of the quasicrystalline i-Al–Cu–Fe alloy grown by molecular beam epitaxy. Using scanning tunneling microscopy and spectroscopy (STM/STS), we mapped the local electron density of states (LDOS) near the film surface with atomic resolution.
In this paper, the electrical conductivity of thin i-Al–Cu–Fe layers is considered. Thin films with a minimum thickness of 125 Å were created by successive deposition and subsequent annealing. The temperature dependence of electrical conductivity at low T, as well as magnetoresistance, were studied. Clear evidence of a change in the nature of quantum interference from three-dimensional to two-dimensional was found when the layer thickness was reduced to a value of≅103 Å.
Complex interference patterns consisting of concentric rings and radial rays radiating from defects and grain boundaries were detected in the STM images. STS measurements showed that these interference structures are associated with features in the LDOS near the Fermi energy. Analysis of the Fourier transform of the STM images revealed the presence of scattering vectors corresponding to the quasi-periodic lattice of i-Al–Cu–Fe.
Our results indicate that electrons in i-Al–Cu–Fe thin films experience strong interference due to scattering on the quasi-periodic potential. This leads to the formation of complex interference patterns in LDOS and may be related to the unusual transport properties of quasicrystals. Further studies are aimed at studying the influence of temperature and magnetic field on the observed interference effects.
Author: T Grenet, F Giroud
Institute: LEPES-CNRS, PO Box 166, 38042 Grenoble, France