218 research outputs found
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
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
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
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.
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
Probing the band structure of quadri-layer graphene with magneto-phonon resonance
We show how the magneto-phonon resonance, particularly pronounced in sp2
carbon allotropes, can be used as a tool to probe the band structure of
multilayer graphene specimens. Even when electronic excitations cannot be
directly observed, their coupling to the E2g phonon leads to pronounced
oscillations of the phonon feature observed through Raman scattering
experiments with multiple periods and amplitudes detemined by the electronic
excitation spectrum. Such experiment and analysis have been performed up to 28T
on an exfoliated 4-layer graphene specimen deposited on SiO2, and the observed
oscillations correspond to the specific AB stacked 4-layer graphene electronic
excitation spectrum.Comment: 11 pages, 5 Fi
Circular dichroism of magneto-phonon resonance in doped graphene
Polarization resolved, Raman scattering response due to E phonon in
monolayer graphene has been investigated in magnetic fields up to 29 T. The
hybridization of the E phonon with only the fundamental inter Landau
level excitation (involving the n=0 Landau level) is observed and only in one
of the two configurations of the circularly crossed polarized excitation and
scattered light. This polarization anisotropy of the magneto-phonon resonance
is shown to be inherent to relatively strongly doped graphene samples, with
carrier concentration typical for graphene deposited on SiO
The hole Fermi surface in BiSe probed by quantum oscillations
Transport and torque magnetometry measurements are performed at high magnetic
fields and low temperatures in a series of p-type (Ca-doped) BiSe
crystals. The angular dependence of the Shubnikov-de Haas and de Haas-van
Alphen quantum oscillations enables us to determine the Fermi surface of the
bulk valence band states as a function of the carrier density. At low density,
the angular dependence exhibits a downturn in the oscillations frequency
between and , reflecting a bag-shaped hole Fermi surface.
The detection of a single frequency for all tilt angles rules out the existence
of a Fermi surface with different extremal cross-sections down to ~meV.
There is therefore no signature of a camel-back in the valence band of our bulk
samples, in accordance with the direct band gap predicted by calculations.Comment: A supplemental material file giving a more detailed description of
our work is available upon reques
Plasmonic terahertz detectors based on a high-electron mobility GaAs/AlGaAs heterostructure
In order to characterize magnetic-field (B) tunable THz plasmonic detectors,
spectroscopy experiments were carried out at liquid helium temperatures and
high magnetic fields on devices fabricated on a high electron mobility
GaAs/AlGaAs heterostructure. The samples were either gated (the gate of a
meander shape) or ungated. Spectra of a photovoltage generated by THz radiation
were obtained as a function of B at a fixed THz excitation from a THz laser or
as a function of THz photon frequency at a fixed B with a Fourier spectrometer.
In the first type of measurements, the wave vector of magnetoplasmons excited
was defined by geometrical features of samples. It was also found that the
magnetoplasmon spectrum depended on the gate geometry which gives an additional
parameter to control plasma excitations in THz detectors. Fourier spectra
showed a strong dependence of the cyclotron resonance amplitude on the
conduction-band electron filling factor which was explained within a model of
the electron gas heating with the THz radiation. The study allows to define
both the advantages and limitations of plasmonic devices based on high-mobility
GaAs/AlGaAs heterostructures for THz detection at low temperatures and high
magnetic fields.Comment: 8 pages, 11 figure
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