Why is CNT considered a 1D structure despite having movement in two dimensions?

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Halaaku
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The electronic structure of CNT is discussed on the basis of band structure of
graphene. Graphene has a linear dispersion relation:
E = h_cut vF |k|
where k is the 2D wavevector and vF is the Fermi velocity. CNTs are
macroscopic along the axis but have a circumference of atomic dimensions, which
suggests that there will be large states in the axial direction but quantized
circumferential states. this implies that there are allowed transitions between circumferential states such that the movement is in the direction perpendicular to the axial direction of CNT. Therefore the movement is in two dimensions, yet we say CNT is a 1D structure. Why is that the case?
 
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The second dimension does not appear as "dimension" - the electrons do not move in that direction, even if it might give additional energy levels (depending on the temperature).