Magnetorotons in quasi-one-dimensional electron systems in the absence of Kohn's theorem

Using a time-dependent Hartree-Fock approximation we have investigated the inter-Landau-level collective excitation spectrum of quasi-one-dimensional electron gases where Kohn's theorem is violated. We find that the spectrum develops a roton minimum at finite wave vectors. In addition to the main magnetoroton, extra collective modes are found. Also we find that it is important to include both the Hartree and exchange local-field corrections in a calculation of the cyclotron resonance.