Bandgap modulation of quasi-metallic carbon nanotubes in a transverse electric field

– We propose a method to modulate the bandgaps in quasi-metallic carbon nanotubes using a transverse electric field. Unlike previous investigations, we include curvature effects of the nanotubes by incorporating both πand σ-orbitals in our tight-binding calculations. The calculations show that the small curvature-induced bandgaps decrease quadratically with electric field amplitude to zero. As the electric field amplitude continues to increase, the bandgap then expands in a similar manner to that presented in earlier studies. The bandgap dependence is verified by analytical calculations, which also agree with preceding analyses for the limit of no curvature. The electronic properties of single-walled carbon nanotubes (SWCNTs) have features making them suitable for a range of applications in quantum information processing and spintronics. Central to these potential applications is the energy dispersion. It has been predicted [1,2] and shown [3, 4] that SWCNTs can be metallic as well as semiconducting. Transport experiments have demonstrated single-electron [5, 6] and field-effect [7, 8] transistor action, among several other interesting physical effects. In these experiments gates have been applied to shift the electrostatic potential on the nanotubes; however, split gate structures can also be used to create electric fields. These fields are known to couple bands in the energy dispersion [9–14]. If the split gates are deposited at different points along a SWCNT, artificial heterojunctions can be created and different types of quantum dot arrays can be produced. Gated structures of this kind have been fabricated for multi-walled carbon nanotubes [15]. The electronic properties of SWCNTs are normally determined by their chiral vector elements (n,m) (see refs. [3, 4] for a complete definition and experimental justification). Nanotubes satisfying n−m = 3p, where p is an integer, have become conventionally known as metallic nanotubes. However, most metallic nanotubes are in fact small bandgap semiconductors