Electrical Switching in Metallic Carbon Nanotubes

Abstract

We present first-principles calculations of quantum transport which show that the resistance of metallic carbon nanotubes can be changed dramatically with homogeneous transverse electric fields if the nanotubes have impurities or defects. The change of the resistance is predicted to range over more than two orders of magnitude with experimentally attainable electric fields. This novel property has its origin that backscattering of conduction electrons by impurities or defects in the nanotubes is strongly dependent on the strength and/or direction of the applied electric fields. We expect this property to open a path to new device applications of metallic carbon nanotubes.PACS numbers: 72.80. Rj, 73.63.Fg, 81.05.Tp Are single-walled carbon nanotubes (SWNTs) suitable for future nano-electronic device applications? The answer depends on whether the electrical properties of carbon nanotubes are changeable by applied gate voltages or electric fields [1]. Carbon nanotubes are either semiconducting or metallic, depending on their atomic geometry (diameter and chirality). Semiconducting carbon nanotubes are well suited for nano-electronic device applications [2,3,4,5] because their electrical resistance is controllable by the gate voltage just as in silicon-based field-effect transistors. On the other hand, metallic nanotubes reportedly have electrical resistances which are not sensitive to the gate voltage or homogeneous transverse electric fields [6,7,8,9] and this insensitivity has discouraged device applications of the metallic ones. The previous reports on metallic nanotubes, however, are limited to clean ones with electric fields [8,9,10,11,12] or to defective ones without electric fields [13,14,15,16] even though impurities or structural defects under the transverse electric field may produce exotic effects because of the low dimensionality of the nanotubes.A clean armchair-type SWNT is metallic with two linear bands intersecting at the Fermi energy (E F ) regardless of its diameter [17] (Fig. 1(a)). The tube's electrical resistance is determined by its electronic structure. A clean metallic SWNT should have an electrical resistance of 6.5 kΩ in two-probe measurements with perfect electrical contacts [17,18]. This results from the resistance quantum, 12.9 kΩ [19,20] (which is h/2e 2 with h = Planck's constant and e = charge of an electron) divided by the number of bands at E F . The resistance of a clean metallic carbon nanotube is insensitive to a homogeneous transverse (i.e., perpendicular to the tubular axis) electric field. Although the applied electric field polarizes the nanotube along the field direction [21] and the band dispersion is modified near E F (Fermi velocities are slightly decreased as shown in Fig. 1(b)), electric fields of moderate strength do not change the number of bands at E F [8, 9, 10, 11] which is the only material parameter that determines the resistance of a clean one dimensional sample. Contrary to the clean tube case, however, a defective metallic carbon nanotube, as will be show...

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