The two classes of low energy spectra in finite carbon nanotubes

Abstract

Electrons in carbon nanotubes (CNTs) possess spin and orbital degrees of freedom. The latter is inherited from the bipartite graphene lattice with two inequivalent Dirac points. The electronic spectra obtained in several transport experiments on CNT quantum dots in parallel magnetic field often show an anticrossing of spectral lines assigned to the opposite Dirac valleys. So far this valley mixing has been attributed to the disorder, with impurity induced scattering. We show that this effect can arise also in ultraclean CNTs of the armchair class and it can be caused solely by the presence of the boundaries. In contrast, in CNTs of the zigzag class it does not occur. These two fundamentally different classes of spectra arise because of different symmetries of the low energy eigenstates of the two types of CNTs. The magnitude of the level splitting depends in a nonmonotonous way on the distance of the involved energy levels from the charge neutrality point.

5 pages, 4 figures, available Supplementary Material

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• Blocking transport resonances via Kondo entanglement in quantum dots
• Topology and zero energy edge states in carbon nanotubes with superconducting pairing
• Secondary electron interference from trigonal warping in clean carbon nanotubes
• Kondo effect in a carbon nanotube with spin-orbit interaction and valley mixing: A DM-NRG study
• Metallic Carbon Nanotube Quantum Dots with Broken Symmetries as a Platform for Tunable Terahertz Detection
• Transverse profile and 3D spin canting of a Majorana state in carbon nanotubes
• Spin-orbit coupling and proximity effects in metallic carbon nanotubes
• Quantum noise in carbon nanotubes as a probe of correlations in the Kondo regime
• Staggered spin-orbit interaction in a nanoscale device