857 research outputs found
Magnetic-field-induced Stoner transition in a dilute quantum Hall system
In a recent paper [Phys.Rev.B.\textbf{84}, 161307 (2011)], experimental data
on spin splitting in the integer quantum Hall effect has been reported in a
high mobility dilute 2D electron gas with electron density as low as 0.2
10 cm . In this work, we show that an excellent
\emph{quantitative} description of these data can be obtained within the model
of the magnetic-field-induced Stoner transition in the quantum Hall regime.
This provides a powerful tool to probe the non-trivial density dependance of
electron-electron interactions in the dilute regime of the 2D electron gas
Quasiparticle density of states in BiSrCaCuO single crystals probed using tunneling spectroscopy at ultra-low temperatures in high magnetic fields
Break-junction tunneling spectroscopy at temperatures 30-50 mK in high
magnetic field is used to directly probe the quasiparticle density of states
within the energy gap in a single crystal Bi2212 high- superconductor. The
measured tunneling conductances in the subgap region have a zero
flat region with no evidence for a linear increase of the density of states
with voltage. A number of tunnel break-junctions exhibited curves
with a second energy gap structure at the average magnitude 2 mV. Our data cannot be explained by either a pure pairing or a
pure pairing
Interplay among spin, orbital effects and localization in a GaAs two-dimensional electron gas in a strong in-plane magnetic field
The magnetoresistance of a low carrier density, disordered GaAs based
two-dimensional (2D) electron gas has been measured in parallel magnetic fields
up to 32 T. The feature in the resistance associated with the complete spin
polarization of the carriers shifts down by more than 20 T as the electron
density is reduced, consistent with recent theories taking into account the
enhancement of the electron-electron interactions at low densities.
Nevertheless, the magnetic field for complete polarization, Bp, remains 2-3
times smaller than predicted for a disorder free system. We show, in particular
by studying the temperature dependance of Bp to probe the effective size of the
Fermi sea, that localization plays an important role in determining the spin
polarization of a 2D electron gas.Comment: Published in the 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
Using the de Haas-van Alphen effect to map out the closed three-dimensional Fermi surface of natural graphite
The Fermi surface of graphite has been mapped out using de Haas van Alphen
(dHvA) measurements at low temperature with in-situ rotation. For tilt angles
between the magnetic field and the c-axis, the majority
electron and hole dHvA periods no longer follow the behavior
demonstrating that graphite has a 3 dimensional closed Fermi surface. The Fermi
surface of graphite is accurately described by highly elongated ellipsoids. A
comparison with the calculated Fermi surface suggests that the SWM trigonal
warping parameter is significantly larger than previously thought
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
In-plane current-voltage characteristics and oscillatory Josephson-vortex flow resistance in La-free BiSrCuO single crystals in high magnetic fields
We have investigated the in-plane characteristics and the Josephson
vortex flow resistance in high-quality La-free
BiSrCuO (Bi2201) single crystals in parallel and
tilted magnetic fields at temperatures down to 40 mK. For parallel magnetic
fields below the resistive upper critical field , the
characteristic obey a power-law with a smooth change with increasing
magnetic-field of the exponent from above 5 down to 1. In contrast to the
double-layer cuprate Bi2212, the observed smooth change suggests that there is
no change in the mechanism of dissipation (no Kosterlitz-Thouless transition)
over the range of temperatures investigated. At small angles between the
applied field and the -plane, prominent current steps in the
characteristics and periodic oscillations of Josephson-vortex flow resistance
are observed. While the current steps are periodic in the voltage at constant
fields, the voltage position of the steps, together with the flux-flow voltage,
increases nonlinearly with magnetic field. The -flow resistance oscillates
as a function of field with a constant period over a wide range of magnetic
fields and temperatures. The current steps in the characteristics and
the flow resistance oscillations can be linked to the motion of Josephson
vortices across layers
Second order resonant Raman scattering in single layer tungsten disulfide (WS)
Resonant Raman spectra of single layer WS flakes are presented. A
second order Raman peak (2LA) appears under resonant excitation with a
separation from the E mode of only cm. Depending on the
intensity ratio and the respective line widths of these two peaks, any analysis
which neglects the presence of the 2LA mode can lead to an inaccurate
estimation of the position of the E mode, leading to a potentially
incorrect assignment for the number of layers. Our results show that the
intensity of the 2LA mode strongly depends on the angle between the linear
polarization of the excitation and detection, a parameter which is neglected in
many Raman studies.Comment: 6 pages, 4 figure
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