12 research outputs found
Effects of electron-electron interactions on the electronic Raman scattering of graphite in high magnetic fields
We report the observation of strongly temperature-dependent, asymmetric
spectral lines in electronic Raman scattering spectra of graphite in a high
magnetic field up to 45 T applied along the c-axis. The magnetic field
quantizes the in-plane motion, while the out-of-plane motion remains free,
effectively reducing the system dimension from three to one. Optically created
electron-hole pairs interact with, or shake up, the one-dimensional Fermi sea
in the lowest Landau subbands. Based on the Tomonaga-Luttinger liquid theory,
we show that interaction effects modify the van Hove singularity to the form
at zero temperature. At finite temperature, we
predict a thermal broadening factor that increases linearly with the
temperature. Our model reproduces the observed temperature-dependent
line-shape, determining to be 0.05 at 40 T
Magnetophonon resonance in graphite: High-field Raman measurements and electron-phonon coupling contributions
We perform Raman scattering experiments on natural graphite in magnetic fields up to 45 T, observing a series of peaks due to interband electronic excitations over a much broader magnetic field range than previously reported. We also explore electron-phonon coupling in graphite via
magnetophonon resonances
Measurement of filling-factor-dependent magnetophonon resonances in graphene using Raman spectroscopy.
We perform polarization-resolved Raman spectroscopy on graphene in magnetic fields up to 45 T. This reveals a filling-factor-dependent, multicomponent anticrossing structure of the Raman G peak, resulting from magnetophonon resonances between magnetoexcitons and E(2g) phonons. This is explained with a model of Raman scattering taking into account the effects of spatially inhomogeneous carrier densities and strain. Random fluctuations of strain-induced pseudomagnetic fields lead to increased scattering intensity inside the anticrossing gap, consistent with the experiments
Dual-gated bilayer graphene hot electron bolometer
Detection of infrared light is central to diverse applications in security,
medicine, astronomy, materials science, and biology. Often different materials
and detection mechanisms are employed to optimize performance in different
spectral ranges. Graphene is a unique material with strong, nearly
frequency-independent light-matter interaction from far infrared to
ultraviolet, with potential for broadband photonics applications. Moreover,
graphene's small electron-phonon coupling suggests that hot-electron effects
may be exploited at relatively high temperatures for fast and highly sensitive
detectors in which light energy heats only the small-specific-heat electronic
system. Here we demonstrate such a hot-electron bolometer using bilayer
graphene that is dual-gated to create a tunable bandgap and
electron-temperature-dependent conductivity. The measured large electron-phonon
heat resistance is in good agreement with theoretical estimates in magnitude
and temperature dependence, and enables our graphene bolometer operating at a
temperature of 5 K to have a low noise equivalent power (33 fW/Hz1/2). We
employ a pump-probe technique to directly measure the intrinsic speed of our
device, >1 GHz at 10 K.Comment: 5 figure
Raman spectroscopy of graphite in high magnetic fields: Electron-phonon coupling and magnetophonon resonance
The magneto-Raman measurements of graphite were performed in a back-scattering Faraday geometry at temperature 10 K in magnetic fields up to 45 T. The experimental data reveal the rich structure of Raman-active excitations dominated by K-point massive electrons. At high magnetic fields the graphite E2g Raman line shows complex multi- component behavior interpreted as magnetophonon resonance coupled electron-phonon modes at graphite's K-point. Also we found the clear signature of the fundamental, strongly dumped, n=0 magnetophonon resonance associated with H point massless holes. © 2013 AIP Publishing LLC
Aperiodic tilings on the computer
We briefly review the standard methods used to construct quasiperiodic tilings, such as the projection, the inflation, and the grid method. A number of sample Mathematica programs, implementing the different approaches for one- and two-dimensional examples, are discussed. Apart from small examples, the corresponding programs are not contained in the text, but will be made available in electronic form