Exploring the magnetoroton excitations in quantum wires: Inverse dielectric functions

A theoretical investigation has been made of the magnetoplasmon excitations in a quantum wire characterized by a confining harmonic potential and subjected to a perpendicular magnetic field. We study the (nonlocal, dynamic) inverse dielectric function to examine the charge-density excitations within a two-subband model in the framework of Bohm-Pines' random-phase approximation. A particular stress is put on the (intersubband) magnetoroton excitation which changes the sign of its group velocity twice before merging with the respective single-particle continuum. It has already been suggested that the electronic device based on such magnetoroton excitations can act as an {\it active} laser medium [see, e.g., Phys. Rev. B {\bf 78}, 153306 (2008)]. Scrutinizing the real and imaginary parts of the inverse dielectric function provides us with an important information on the longitudinal and transverse (Hall) resistances of the system.