Ab initio band structure of quasi-metallic carbon nanotubes for terahertz applications

P N D’yachkov, I A Bochkov
COMPUTER MODELLING & NEW TECHNOLOGIES 2018 22(1) 7-19
Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii Pr. 31, Moscow 119991, Russia

Two integers (n1, n2) determine the band structure of single-walled carbon nanotubes (CNTs). According to π-electron zone-folding model, an energy gap between the valence and conduction bands disappears if a difference n1 ‒ n2 = 3q is divisible by three. Such CNTs are called the quasi-metallic tubules. An account of surface curvature of tubules predicts that a small gap opens in such CNTs and they are the narrow-gap semiconductors really. Available experimental and theoretical information on the gap energies is very limited. In this paper, the band structures of the 50 CNTs (n1, n2) with 4 ≤ n1 ≤ 18 and n2 = n1 ‒ 3q are calculated using a linearized augmented cylindrical waves method. The quasi-metallic CNTs with optical gaps falling within the terahertz range (1 - 40 meV) are identified, which can be used to design the high-frequency devices like the terahertz emitters, detectors, multipliers, antennas, polarizers, and transistors.