112 research outputs found
Photoluminescence Detected Doublet Structure in the Integer and Fractional Quantum Hall Regime
We present here the results of polarized magneto-photoluminescence
measurements on a high mobility single-heterojunction. The presence of a
doublet structure over a large magnetic field range (2>nu>1/6) is interpreted
as possible evidence for the existence of a magneto-roton minima of the charged
density waves. This is understood as an indication of strong electronic
correlation even in the case of the IQHE limit.Comment: submitted to Solid State Communication
A cascade of magnetic field induced spin transitions in LaCoO3
We present magnetization and magnetostriction studies of the insulating
perovskite LaCoO3 in magnetic fields approaching 100 T. In marked contrast with
expectations from single-ion models, the data reveal two distinct first-order
spin transitions and well-defined magnetization plateaux. The magnetization at
the higher plateau is only about half the saturation value expected for spin-1
Co3+ ions. These findings strongly suggest collective behavior induced by
strong interactions between different electronic -- and therefore spin --
configurations of Co3+ ions. We propose a model of these interactions that
predicts crystalline spin textures and a cascade of four magnetic phase
transitions at high fields, of which the first two account for the experimental
data.Comment: 5 pages + supplementary materials, 5 figure
Circular-Polarization Dependent Cyclotron Resonance in Large-Area Graphene in Ultrahigh Magnetic Fields
Using ultrahigh magnetic fields up to 170 T and polarized midinfrared
radiation with tunable wavelengths from 9.22 to 10.67 um, we studied cyclotron
resonance in large-area graphene grown by chemical vapor deposition.
Circular-polarization dependent studies reveal strong p-type doping for
as-grown graphene, and the dependence of the cyclotron resonance on radiation
wavelength allows for a determination of the Fermi energy. Thermal annealing
shifts the Fermi energy to near the Dirac point, resulting in the simultaneous
appearance of hole and electron cyclotron resonance in the magnetic quantum
limit, even though the sample is still p-type, due to graphene's linear
dispersion and unique Landau level structure. These high-field studies
therefore allow for a clear identification of cyclotron resonance features in
large-area, low-mobility graphene samples.Comment: 9 pages, 3 figure
The High Magnetic Field Phase Diagram of a Quasi-One Dimensional Metal
We present a unique high magnetic field phase of the quasi-one dimensional
organic conductor (TMTSF)ClO. This phase, termed "Q-ClO", is
obtained by rapid thermal quenching to avoid ordering of the ClO anion. The
magnetic field dependent phase of Q-ClO is distinctly different from that
in the extensively studied annealed material. Q-ClO exhibits a spin density
wave (SDW) transition at 5 K which is strongly magnetic field
dependent. This dependence is well described by the theoretical treatment of
Bjelis and Maki. We show that Q-ClO provides a new B-T phase diagram in the
hierarchy of low-dimensional organic metals (one-dimensional towards
two-dimensional), and describe the temperature dependence of the of the quantum
oscillations observed in the SDW phase.Comment: 10 pages, 4 figures, preprin
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Photoluminescence studies of modulation doped coupled double quantum wells in magnetic fields
We have studied the photoluminescence spectra of a series of mudulation doped couple double quantum well structures in parallel and perpendicular magnetic fields to 62 tesla at 4K and 77K, for B{parallel}a, the spectra display distinct Landau level transitions which show anti-crossing with the e1-hh1 exciton. At high fields, the lowest conduction band-valence exciton approaches the extrapolated 0- 0 Landau level. About 25 Tesla, there is valence band mixing of the e1-lh1, e1-hh2, e1-hh1 transitions. The spectral peaks display a diamagnetic shift in low in-plane magnetic fields which become linear in high fields. At magnetic fields beyond 40T, spin splitting is observed for both B{parallel}z and B{perpendicular} geometries. The partial energy gap discovered in conductance measurements in in-plane fields was not conclusively observed using photoluminescence spectroscopy, although anomalies in the energy dependence of the lowest level with magnetic field were evident at similar field values
Fully connected bulk Pb 1−
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Magnetic susceptibility of the normal-superconducting transition in high-purity single-crystal α-uranium
We report complex ac magnetic susceptibility measurements of a superconducting transition in very high-quality single-crystal alpha-uranium using microfabricated coplanar magnetometers. We identify an onset of superconductivity at Tapproximate to0.7 K in both the real and imaginary components of the susceptibility which is confirmed by resistivity data. A superconducting volume fraction argument, based on a comparison with a calibration YBa2Cu3O7-delta sample, indicates that superconductivity in these samples may be filamentary. Our data also demonstrate the sensitivity of the coplanar micro-magnetometers, which are ideally suited to measurements in pulsed magnetic fields exceeding 100 T
Experimental determination of B-T phase diagram of YBa_2Cu_3O_7-d to 150T for B perpendicular to c
The B-T phase diagram for thin film YBa_2Cu_3O_7-d with B parallel to the
superconducting layers has been constructed from GHz transport measurements to
150T. Evidence for a transition from a high T regime dominated by orbital
effects, to a low T regime where paramagnetic limiting drives the quenching of
superconductivity, is seen. Up to 110T the upper critical field is found to be
linear in T and in remarkable agreement with extrapolation of the longstanding
result of Welp et al arising from magnetisation measurements to 6T. Beyond this
a departure from linear behaviour occurs at T=74K, where a 3D-2D crossover is
expected to occur.Comment: 4 pages, 4 figure
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