We consider a ladder model of DNA for describing carrier transport in a fully coherent regime through finite segments. A single orbital is associated to each base, and both interstrand and intrastrand overlaps are considered within the nearest-neighbor approximation. Conduction through the sugar-phosphate backbone is neglected. We study analytically and numerically the spatial extend of the corresponding states by means of the Landauer and Lyapunov exponents. We conclude that intrinsic-DNA correlations, arising from the natural base pairing, does not suffice to observe extended states, in contrast to previous claims.
A two-component superlattice film of 2N layers is considered and a dimensionally quantized spectrum of phonons is found. The problem of localization of phonons in the superlattice with random-thickness layers is investigated. The Landauer resistance of the transport of phonons and the correlation length is calculated exactly. For short range disorder the numerical analyses shows that, at frequency ϭ0, there is a delocalized state and the correlation length index is equal to 2.
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