291 research outputs found
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
3D Dirac semimetal Cd3As2: A review of material properties
Cadmium arsenide (Cd3As2) - a time-honored and widely explored material in
solid-state physics - has recently attracted considerable attention. This was
triggered by a theoretical prediction concerning the presence of 3D
symmetry-protected massless Dirac electrons, which could turn Cd3As2 into a 3D
analogue of graphene. Subsequent extended experimental studies have provided us
with compelling experimental evidence of conical bands in this system, and
revealed a number of interesting properties and phenomena. At the same time,
some of the material properties remain the subject of vast discussions despite
recent intensive experimental and theoretical efforts, which may hinder the
progress in understanding and applications of this appealing material. In this
review, we focus on the basic material parameters and properties of Cd3As2, in
particular those which are directly related to the conical features in the
electronic band structure of this material. The outcome of experimental
investigations, performed on Cd3As2 using various spectroscopic and transport
techniques within the past sixty years, is compared with theoretical studies.
These theoretical works gave us not only simplified effective models, but more
recently, also the electronic band structure calculated numerically using ab
initio methods.Comment: 16 pages, 16 figure
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
Graphite from the viewpoint of Landau level spectroscopy: An effective graphene bilayer and monolayer
We describe an infrared transmission study of a thin layer of bulk graphite
in magnetic fields up to B = 34 T. Two series of absorption lines whose energy
scales as sqrtB and B are present in the spectra and identified as
contributions of massless holes at the H point and massive electrons in the
vicinity of the K point, respectively. We find that the optical response of the
K point electrons corresponds, over a wide range of energy and magnetic field,
to a graphene bilayer with an effective inter-layer coupling 2\gamma_1, twice
the value for a real graphene bilayer, which reflects the crystal ordering of
bulk graphite along the c-axis. The K point electrons thus behave as massive
Dirac fermions with a mass enhanced twice in comparison to a true graphene
bilayer.Comment: 4 pages, 2 figure
Multiple magneto-phonon resonances in graphene
Our low-temperature magneto-Raman scattering measurements performed on
graphene-like locations on the surface of bulk graphite reveal a new series of
magneto-phonon resonances involving both K-point and Gamma-point phonons. In
particular, we observe for the first time the resonant splitting of three
crossing excitation branches. We give a detailed theoretical analysis of these
new resonances. Our results highlight the role of combined excitations and the
importance of multi-phonon processes (from both K and Gamma points) for the
relaxation of hot carriers in graphene.Comment: 20 pages, 11 figure
A micro-magneto-Raman scattering study of graphene on a bulk graphite substrate
We report on a magneto-Raman scattering study of graphene flakes located on
the surface of a bulk graphite substrate. By spatially mapping the Raman
scattering response of the surface of bulk graphite with an applied magnetic
field, we pinpoint specific locations which show the electronic excitation
spectrum of graphene. We present the characteristic Raman scattering signatures
of these specific locations. We show that such flakes can be superimposed with
another flake and still exhibit a graphene-like excitation spectrum.
Two different excitation laser energies (514.5 and 720 nm) are used to
investigate the excitation wavelength dependence of the electronic Raman
scattering signal.Comment: 6 pages, 5 figure
Electronic structure of unidirectional superlattices in crossed electric and magnetic fields and related terahertz oscillations
We have studied Bloch electrons in a perfect unidirectional superlattice
subject to crossed electric and magnetic fields, where the magnetic field is
oriented ``in-plane'', i.e. in parallel to the sample plane. Two orientation of
the electric field are considered. It is shown that the magnetic field
suppresses the intersubband tunneling of the Zener type, but does not change
the frequency of Bloch oscillations, if the electric field is oriented
perpendicularly to both the sample plane and the magnetic field. The electric
field applied in-plane (but perpendicularly to the magnetic field) yields the
step-like electron energy spectrum, corresponding to the magnetic-field-tunable
oscillations alternative to the Bloch ones.Comment: 7 pages, 1 figure, accepted for publication in Phys. Rev.
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