Random-phase Approximation Treatment Of Edge Magnetoplasmons: Edge-state Screening And Nonlocality

A random-phase approximation (RPA) treatment of edge magnetoplasmons (EMP) is presented for strong magnetic fields, low temperatures, and integer filling factors \nu. It is valid for negligible dissipation and lateral confining potentials smooth on the scale of the magnetic length \ell_{0} but sufficiently steep that the Landau-level (LL) flattening can be neglected. LL coupling, screening by edge states, and nonlocal contributions to the current density are taken into account. In addition to the fundamental mode with typical dispersion relation \omega\sim q_x \ln(q_{x}), fundamental modes with {\it acoustic} dispersion relation \omega\sim q_x are obtained for \nu>2. For \nu=1,2 a {\bf dipole} mode exists, with dispersion relation \omega\sim q_x^3, that is directly related to nonlocal responses.Comment: Text 12 pages in Latex/Revtex format, 4 Postscript figure

Repulsion of Single-well Fundamental Edge Magnetoplasmons in Double Quantum Wells

A {\it microscopic} treatment of fundamental edge magnetoplasmons (EMPs) along the edge of a double quantum well (DQW) is presented for strong magnetic fields, low temperatures, and total filling factor \nu=2. It is valid for lateral confining potentials that Landau level (LL) flattening can be neglected. The cyclotron and Zeeman energies are assumed larger than the DQW energy splitting \sqrt{\Delta^2 +4T^2}, where \Delta is the splitting of the isolated wells and T the tunneling matrix element. %hen calculated unperturbed density profile is sharp at the edge. Using a random-phase approximation (RPA), which includes local and nonlocal contributions to the current density, it is shown that for negligible tunnel coupling 2T << \Delta the inter-well Coulomb coupling leads to two DQW fundamental EMPs which are strongly renormalized in comparison with the decoupled, single-well fundamental EMP. These DQW modes can be modified further upon varying the inter-well distance d, along the z axis, and/or the separation of the wells' edges \Delta y along the y axis. The charge profile of the {\it fast} and {\it slow} DQW mode varies, respectively, in an {\it acoustic} and {\it optical} manner along the y axis and is not smooth on the \ell_{0} scale. For strong tunneling \Delta\alt 2T these DQW modes are essentially modified when \Delta is changed by applying a transverse electric field to the DQW.Comment: Text 18 pages in Latex/Revtex/Preprint format, 2 Postscript figure

Role of electronic excitations in magneto-Raman spectra of graphene

We investigate the signature of the low-energy electronic excitations in the Raman spectrum of monolayer and bilayer graphenes. The dominant contribution to the Raman spectra is due to the interband electron-hole (e-h) pairs, which belong to the irreducible representation A(2) of the point group C-6v of the graphene lattice, and are characterized by crossed polarization of incoming and outgoing photons. At high magnetic fields, this is manifested by the excitation of e-h inter-Landau-level (LL) transitions with selection rule n(-) -> n(+). Weaker Raman-active inter-LL modes also exist. One of those has a selection rule similar to the infrared absorption process, n(-) -> (n +/- 1)(+), but the created e-h excitation belongs to the irreducible representation E-2 (rather than E-1) and couples to the optical phonon mode, thus undergoing an anticrossing with the optical phonon G-line in Raman in a strong magnetic field. The fine structure acquired by the G-line due to such anticrossing depends on the carrier density, inhomogeneity of doping and presence of inhomogeneous strain in the sample