Coupled plasmon–LO-phonon modes at high-magnetic fields

Wysmołek, A.; Plantier, D.; Potemski, M.; Słupiński, T.; Żytkiewicz, Z. R.

doi:10.1103/physrevb.74.165206

Cited by 17 publications

(14 citation statements)

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“…Lp, 63.20.Kr, 78.30.Na, Lattice vibrations in solids can be effectively modified via their coupling to electronic excitations, as, for example, evidenced by observations of Kohn anomalies in metals [1,2], of coupled phonon-plasmon modes in polar semiconductors [3,4] or of different phonon spectra in metallic and semiconducting carbon-nanotubes [5]. The electron-phonon interaction is currently intensively studied in graphene [6,7,8,9] which is a two-dimensional crystal of carbon atoms arranged in a honeycomb lattice and a semimetal with characteristic dispersions of electronic states displaying Dirac cones near the Fermi energy [10,11].…”

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Tuning the Electron-Phonon Coupling in Multilayer Graphene with Magnetic Fields

et al. 2009

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Magneto Raman scattering study of the E2g optical phonons in multi-layer epitaxial graphene grown on a carbon face of SiC are presented. At 4.2K in magnetic field up to 33 T, we observe a series of well pronounced avoided crossings each time the optically active inter Landau level transition is tuned in resonance with the E2g phonon excitation (at 196 meV). The width of the phonon Raman scattering response also shows pronounced variations and is enhanced in conditions of resonance. The experimental results are well reproduced by a model that gives directly the strength of the electron-phonon interaction.PACS numbers: 73.22. Lp, 63.20.Kr, 78.30.Na, Lattice vibrations in solids can be effectively modified via their coupling to electronic excitations, as, for example, evidenced by observations of Kohn anomalies in metals [1,2], of coupled phonon-plasmon modes in polar semiconductors [3,4] or of different phonon spectra in metallic and semiconducting carbon-nanotubes [5]. The electron-phonon interaction is currently intensively studied in graphene [6,7,8,9] which is a two-dimensional crystal of carbon atoms arranged in a honeycomb lattice and a semimetal with characteristic dispersions of electronic states displaying Dirac cones near the Fermi energy [10,11]. The case of the long wavelength optical E 2g -phonons at the Γ-point of the Brillouin zone, which corresponds to the relative displacement of two nonequivalent carbon atoms in the unit cell of graphene [6,7], is of particular interest. The perturbation due to this displacement is effective in inducing the direct (∆k = 0) electronic transitions across the Dirac point: E 2g -phonons efficiently couple to those low energy interband excitations [6,7] that are unique to graphene. The spectrum of these excitations (its 2E F low energy onset) can be modified by tuning the Fermi energy E F . This was achieved in gated graphene flakes on Si/SiO 2 substrates where the electrically modified E 2g -phonon spectrum was traced with Raman scattering methods [8,9].The spectrum of the graphene E 2g -phonon is expected to be even more severely modified by applying a magnetic field perpendicular to the 2D plane [12,13], i.e., when a continuous spectrum of electronic excitations is transformed into a series of quasi-discrete inter Landau level excitations characteristic of a 2D system. In conditions of Landau quantization, the electron phonon coupling has a resonant character which is expected between the E 2g -phonon and properly selected inter-Landau level excitations. The observation of the effects of magneto-resonant electron-phonon coupling in graphene structures, which we present in this letter, has been an experimental challenge [27] aiming at verification of theoretical predictions [12,13] and eventual confirmation of the conclusions drawn from zero-field measurements [8,9].We report here on magneto-Raman scattering studies of the E 2g -phonon band of multilayer epitaxial graphene on the carbon face of a SiC substrate (MEG), in fields up to 33 T, and low, liquid helium temp...

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Tuning the Electron-Phonon Coupling in Multilayer Graphene with Magnetic Fields

et al. 2009

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“…The detailed analysis of the Raman scattering data obtained for GaAs samples of different electron concentrations, including nonlocal effects responsible for the interaction with finite k-vector modes is presented in Ref. [26]. The experimental data obtained for samples, within the wide range of electron concentrations, can be reasonably well described using the standard approach of the longitudinal dielectric function but including nonlocal effects.…”

Section: Limit Of High Electron Concentrationsmentioning

confidence: 92%

“…The application of a magnetic field modifies the measured Raman response, and the effect is remarkably dependent on the configuration of the incident and scattered wave vectors (correspondingly, k i and k s ) with respect to the magnetic field (B) direction [26,27]. Except the effect of field-dependent spectral broadening, the coupled plasmon-phonon modes are little influenced by the magnetic field applied in the backscattering Faraday configuration (see Fig.…”

Section: Limit Of High Electron Concentrationsmentioning

confidence: 99%

“…This simply reflects the anisotropic character of the Lorentz force, which acts on the mobile charges in a magnetic field [26]. The Raman spectra measured versus magnetic field for two samples with high electron concentrations are shown in Fig.…”

Section: Limit Of High Electron Concentrationsmentioning

confidence: 99%

“…It is worth noticing that in a simple approximation, if the effective mass is known and does not depend on the electron concentration, i.e., the effect of nonparabolicity is neglected, a knowledge of the energies of ω − and ω + modes provides a very direct estimate of the electron concentration in the sample [26].…”

Section: Zero Field Raman Spectra On N-type Gaasmentioning

confidence: 99%

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Magnetized Plasma in Polar Semiconductors

Wysmołek

2007

Acta Phys. Pol. A

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Plasma excitations in metallic n-type GaAs are studied in high-magnetic fields using the method of inelastic light scattering (the Raman scattering). Experimental data are analyzed using a standard, dielectric function theory. The results obtained for samples with a high electron concentration are well understood in terms of longitudinal excitations. A strong interaction of coupled longitudinal optical-phonon-plasmon modes with the collective cyclotron resonance excitations (the Bernstein modes) is observed. In samples with a lower electron concentration, the unexpected feature in the vicinity of the undressed optical phonon is observed at high magnetic fields. This effect is explained in terms of transverse excitations, which would appear in the Raman spectrum due to disorder-activated selection-rule breaking. A field induced metal-insulator transition and magnetopolaron effect on shallow donors in GaAs is shown to be traced with the Raman scattering experiments in samples with the lowest electron concentration.

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