In this work, we use the tight-binding model to study the low-energy electronic properties of telescoping double-walled carbon nanotubes subject to the influences of a transverse electric field and a parallel magnetic field. The state energy and energy spacings are found to oscillate significantly with the overlapping length. External fields would modify the state energies, alter the energy gaps, and destroy the state degeneracy. Complete energy gap modulations can be accomplished either by varying the overlapping length, or by applying an electric field or a magnetic field. The variations of state energies with the external fields will be directly reflected in the density of states. The numbers, heights, and frequencies of the density of states peaks are strongly dependent on the external fields. (C) 2007 Elsevier Ltd. All rights reserved.
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