Single-particle subband properties of quantum cables

We proposed a new kind of coupled coaxial cylindrical quantum wires structure - quantum cable, and calculated its single-electron energy subband spectrum for the varying structure parameters, in order to investigate its subband motion in the structure parameter space. It is shown that quantum cable has unique subband spectrum, which differs either from the (solid and hollow) cylindrical quantum wire or from the usual coupled double quantum wires (CDQWs) structure. Aside from the two-fold degeneracy induced by the cylindrical symmetry, crossings (accidental degeneracies) and anticrossings (repulsions) of quantum cable subbands with different azimuthal and radial quantum numbers are observed as one of the cable structure parameters varies. This introduces the dependence of the subband ladder on the structure parameters of the quantum cable structure. However, the subband with the lowest azimuthal and radial quantum numbers remains the lowest subband and never crosses with the other subbands irrespective of the value of structure parameters. As the coupling barrier is broadening (coupling becoming weak), some subbands bundling toward another subband is seen before the extreme isolating limit achieved. Moreover, the separation between neighboring subbands exhibits non-monotonous evolution as one changes the thickness of one of the cylindrical quantum wires, with a minimum existing in the separation between some two adjacent subbands. Interesting optical and transport phenomena arising from these unique subband properties of the quantum cable structure are also predicted.