Evanescent channels and scattering in cylindrical nanowire heterostructures

We investigate the scattering phenomena produced by a general finite-range nonseparable potential in a multichannel two-probe cylindrical nanowire heterostructure. The multichannel current scattering matrix is efficiently computed using the $R$-matrix formalism extended for cylindrical coordinates. Considering the contribution of the evanescent channels to the scattering matrix, we are able to put in evidence the specific dips in the tunneling coefficient in the case of an attractive potential. The cylindrical symmetry cancels the ``selection rules'' known for Cartesian coordinates. If the attractive potential is superposed over a nonuniform potential along the nanowire then resonant transmission peaks appear. We can characterize them quantitatively through the poles of the current scattering matrix. Detailed maps of the localization probability density sustain the physical interpretation of the resonances (dips and peaks). Our formalism is applied to a variety of model systems such as a quantum dot, a core/shell quantum ring, or a double barrier embedded into the nanocylinder.