497 research outputs found
Quadexciton cascade and fine structure splitting of the triexciton in a single quantum dot
We report the properties of emission lines associated with the cascaded
recombination of a quadexciton in single GaAlAs/AlAs quantum dots, studied by
means of polarization-resolved photoluminescence and single-photon correlation
experiments. It is found that photons which are emitted in a double-step 4X-3X
process preserve their linear polarization, similarly to the case of conserved
polarization of correlated photons in the 2X-X cascade. In contrast, an
emission of either co-linear or cross-linear pairs of photons is observed for
the 3X-2X cascade. Each emission line associated with the quadexciton cascade
shows doublet structure in the polarization-resolved photoluminescence
experiment. The maximum splitting is seen when the polarization axis is chosen
along and perpendicular to the [110] crystallographic direction. This effect is
ascribed to the fine structure splitting of the exciton and triexciton states
in the presence of an anisotropic confining potential of ae dot. We also show
that the splitting in the triexciton state surpasses that in the exciton state
by a factor up to eight and their ratio scales with the energy distance between
the 3X and X emission lines, thus, very likely, with a lateral size and/or a
composition of the dot.Comment: submitted to Physical Review
A consistent interpretation of the low temperature magneto-transport in graphite using the Slonczewski--Weiss--McClure 3D band structure calculations
Magnetotransport of natural graphite and highly oriented pyrolytic graphite
(HOPG) has been measured at mK temperatures. Quantum oscillations for both
electron and hole carriers are observed with orbital angular momentum quantum
number up to . A remarkable agreement is obtained when comparing
the data and the predictions of the Slonczewski--Weiss--McClure tight binding
model for massive fermions. No evidence for Dirac fermions is observed in the
transport data which is dominated by the crossing of the Landau bands at the
Fermi level, corresponding to , which occurs away from the point
where Dirac fermions are expected.Comment: 3 figure
Dirac fermions at the H point of graphite: Magneto-transmission studies
We report on far infrared magneto-transmission measurements on a thin
graphite sample prepared by exfoliation of highly oriented pyrolytic graphite.
In magnetic field, absorption lines exhibiting a blue-shift proportional to
sqrtB are observed. This is a fingerprint for massless Dirac holes at the H
point in bulk graphite. The Fermi velocity is found to be c*=1.02x10^6 m/s and
the pseudogap at the H point is estimated to be below 10 meV. Although the
holes behave to a first approximation as a strictly 2D gas of Dirac fermions,
the full 3D band structure has to be taken into account to explain all the
observed spectral features.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Landau level spectroscopy of ultrathin graphite layers
Far infrared transmission experiments are performed on ultrathin epitaxial
graphite samples in a magnetic field. The observed cyclotron resonance-like and
electron-positron-like transitions are in excellent agreement with the
expectations of a single-particle model of Dirac fermions in graphene, with an
effective velocity of c* = 1.03 x 10^6 m/s.Comment: 4 pages 4 figures Slight revisions following referees' comments. One
figure modifie
Microwave magnetoplasmon absorption by a 2DEG stripe
Microwave absorption by a high mobility 2DEG has been investigated
experimentally using sensitive Electron Paramagnetic Resonance cavity
technique. It is found that MW absorption spectra are chiefly governed by
confined magnetoplasmon excitations in a 2DEG stripe. Spectra of the 2D
magnetoplasmons are studied as a function of magnetic field, MW frequency and
carrier density. The electron concentration is tuned by illumination and
monitored using optical photoluminescence technique.Comment: to be published in International Journal of Modern Physics
Thermal conductivity of graphene in Corbino membrane geometry
Local laser excitation and temperature readout from the intensity ratio of
Stokes to anti-Stokes Raman scattering signals are employed to study the
thermal properties of a large graphene membrane. The concluded value of the
heat conductivity coefficient \kappa ~ 600 W/m \cdot K is smaller than
previously reported but still validates the conclusion that graphene is a very
good thermal conductor.Comment: 4 pages, 3 figure
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