Hydrodynamic theory of intrasubband plasmons in quasi-one-dimensional systems

We use a simple hydrodynamic model to develop a theory of intrasubband plasmons in (quasi-) one-dimensional systems. The derivation gives insights into the relative motion of charge within different subbands, and the results allow easy estimates of the coupling of these modes to either internal or external charges. We compare the hydrodynamic model predictions with those of a microscopic theory, the quantum-mechanical random-phase approximation, both at a formal and at a numerical level. The phenomenological parameters can be chosen so that hydrodynamics reproduces the microscopic results in the long-wavelength limit.