Green-function theory of confined plasmons in coaxial cylindrical geometries: Finite magnetic field

Abstract

We report on a theoretical investigation of plasmon propagation in the coaxial cylindrical geometries using Green-function (or response-function) theory in the presence of an applied axial magnetic field $(\stackrel{P\vec}{B}\ensuremath{\Vert}\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{z})$. The magnetoplasmon excitations in such multiple-interface structures are characterized by the electromagnetic (EM) fields that are localized at and decay exponentially away from the interfaces. Green-function theory, when generalized to be applicable to such quasi-one-dimensional systems, enables us to derive explicit expressions for the corresponding response functions (associated with EM fields), which can in turn be used to compute numerous physical properties of the system under consideration. A rigorous analytical diagnosis of the general results in diverse situations leads us to reproduce exactly the previously well-established results on planar systems, both in the presence and absence of $\stackrel{P\vec}{B}$, obtained within the different theoretical frameworks. As an application, we present several illustrative examples on the dispersion characteristics of the confined and extended magnetoplasmons in the single- and double-interface structures. These dispersive modes are also substantiated through the computation of local as well as total density of states. It is found that, unlike as in the zero-field case, the magnetoplasma propagation is nonreciprocal with respect to the sign of the index $m$ of the Bessel functions involved. The effects of an applied magnetic field and the aspect ratio on the dispersion of the confined magnetoplasmons are discussed. We also briefly clarify some delusive traces of the edge magnetoplasmons for a plasma shell embedded between two identical or unidentical dielectrics. The elegance of theory lies in the fact that it does not require matching of the messsy boundary conditions and it also lies in its simplicity and the compact form of the desired results. Our theoretical framework can also serve as a powerful technique for studying the intrasubband plasmons and magnetoplasmons in the emerging mutiple-walled carbon nanotubes.