Interband transitions in narrow-gap carbon nanotubes and graphene nanoribbons

• Main Authors: Saroka, V. A., Hartmann, R. R., Portnoi, M. E.
• Format: text
• Published: Animo Repository 2019
• Subjects: Carbon nanotubes; Graphene; Physics
• Online Access: https://animorepository.dlsu.edu.ph/faculty_research/3402; https://animorepository.dlsu.edu.ph/context/faculty_research/article/4404/type/native/viewcontent/B978_0_08_102393_8.00004_2
• Institution: De La Salle University

In this chapter, interband dipole transitions are calculated in quasi-metallic single-walled carbon nanotubes. The optical matrix elements in zigzag nanotubes for incident radiation polarized parallel to the axis of the translation symmetry are compared with the corresponding matrix elements in armchair graphene nanoribbons. It is shown that the curvature effects for tubes and the edge effects for ribbons result not only in a small bandgap opening, corresponding to terahertz (THz) frequencies, but also in a significant enhancement of the transition probability rate across the bandgap. The velocity matrix element characterizing the rate of transitions has a universal value equal to the Fermi velocity of electrons in graphene. This makes these nanostructures perspective candidates for sources and detectors of terahertz radiation. A possible terahertz generation scheme is presented and discussed. It is also shown that in gapped honeycomb lattices, additionally to the strong transitions across the bandgap and momentum alignment for linearly polarized light, valley-dependent selection rules also arise for circularly polarized light. © 2019 Elsevier Ltd. All rights reserved.