Artificially Structured Incommensurate Materials
Modern ultrahigh vacuum deposition techniques such as Molecular Beam Epitaxy offer interesting opportunities for the fabrication of materials in which the incommensurate nature of the structure is expected to dominate the physical properties. We have recently demonstrated the MBE growth of heterostructures in which layers of GaAs and AlAs were deposited in a Fibonacci sequence. This yields a quasi-periodic structure with the ratio of incommensurate periods equal to the golden mean, τ. Here we present an overview of the unique structural, electronic, and vibrational properties of this new class of materials emphasizing the role of the incommensurate structure normal to the layers. Inevitably, defects are introduced by growth fluctuations but do not appear to disrupt significantly the special characteristics which originate from the quasiperiodic ordering.
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