702 research outputs found
Genetic Characterization of the Tick-Borne Orbiviruses
The International Committee for Taxonomy of Viruses (ICTV) recognizes four species of tick-borne orbiviruses (TBOs): Chenuda virus, Chobar Gorge virus, Wad Medani virus and Great Island virus (genus Orbivirus, family Reoviridae). Nucleotide (nt) and amino acid (aa) sequence comparisons provide a basis for orbivirus detection and classification, however full genome sequence data were only available for the Great Island virus species. We report representative genome-sequences for the three other TBO species (virus isolates: Chenuda virus (CNUV); Chobar Gorge virus (CGV) and Wad Medani virus (WMV)). Phylogenetic comparisons show that TBOs cluster separately from insect-borne orbiviruses (IBOs). CNUV, CGV, WMV and GIV share low level aa/nt identities with other orbiviruses, in 'conserved' Pol, T2 and T13 proteins/genes, identifying them as four distinct virus-species. The TBO genome segment encoding cell attachment, outer capsid protein 1 (OC1), is approximately half the size of the equivalent segment from insect-borne orbiviruses, helping to explain why tick-borne orbiviruses have a ~1 kb smaller genome
Dynamics of liquid crystalline domains in magnetic field
We study microscopic single domains nucleating and growing within the
coexistence region of the Isotropic (I) and Nematic (N) phases in magnetic
field. By rapidly switching on the magnetic field the time needed to align the
nuclei of sufficiently large size is measured, and is found to decrease with
the square of the magnetic field. When the field is removed the disordering
time is observed to last on a longer time scale. The growth rate of the nematic
domains at constant temperature within the coexistence region is found to
increase when a magnetic field is applied.Comment: 10 pages, 5 figures, unpublishe
Transport Gap in Suspended Bilayer Graphene at Zero Magnetic Field
We report a change of three orders of magnitudes in the resistance of a
suspended bilayer graphene flake which varies from a few ks in the high
carrier density regime to several Ms around the charge neutrality point
(CNP). The corresponding transport gap is 8 meV at 0.3 K. The sequence of
appearing quantum Hall plateaus at filling factor followed by
suggests that the observed gap is caused by the symmetry breaking of the lowest
Landau level. Investigation of the gap in a tilted magnetic field indicates
that the resistance at the CNP shows a weak linear decrease for increasing
total magnetic field. Those observations are in agreement with a spontaneous
valley splitting at zero magnetic field followed by splitting of the spins
originating from different valleys with increasing magnetic field. Both, the
transport gap and field response point toward spin polarized layer
antiferromagnetic state as a ground state in the bilayer graphene sample. The
observed non-trivial dependence of the gap value on the normal component of
suggests possible exchange mechanisms in the system.Comment: 8 pages, 5 figure
Linear magnetoresistance in a quasi-free two dimensional electron gas in an ultra-high mobility GaAs quantum well
We report a magnetotransport study of an ultra-high mobility
(\,cm\,V\,s) -type GaAs
quantum well up to 33 T. A strong linear magnetoresistance (LMR) of the order
of 10 % is observed in a wide temperature range between 0.3 K and 60 K. The
simplicity of our material system with a single sub-band occupation and free
electron dispersion rules out most complicated mechanisms that could give rise
to the observed LMR. At low temperature, quantum oscillations are superimposed
onto the LMR. Both, the featureless LMR at high and the quantum
oscillations at low follow the empirical resistance rule which states that
the longitudinal conductance is directly related to the derivative of the
transversal (Hall) conductance multiplied by the magnetic field and a constant
factor that remains unchanged over the entire temperature range. Only
at low temperatures, small deviations from this resistance rule are observed
beyond that likely originate from a different transport mechanism for
the composite fermions
Electron-phonon coupling in the two phonon mode ternary alloy quantum well
We have investigated the infrared transmission of a two-dimensional (2DEG)
electron gas confined in a single
quantum well in order to study the electron optical phonon interaction in a two
phonon mode system. Infrared transmission experiments have been performed in
both the perpendicular Faraday (PF) and tilted Faraday (TF) configurations for
which the growth axis of the sample is tilted with respect to the incident
light propagation direction and to the magnetic field direction. The
experimental results lead to question the validity of the concept of polaron
mass in a real material.Comment: 7 pages, 3 figure
Lifting of the Landau level degeneracy in graphene devices in a tilted magnetic field
We report on transport and capacitance measurements of graphene devices in
magnetic fields up to 30 T. In both techniques, we observe the full splitting
of Landau levels and we employ tilted field experiments to address the origin
of the observed broken symmetry states. In the lowest energy level, the spin
degeneracy is removed at filling factors and we observe an enhanced
energy gap. In the higher levels, the valley degeneracy is removed at odd
filling factors while spin polarized states are formed at even . Although
the observation of odd filling factors in the higher levels points towards the
spontaneous origin of the splitting, we find that the main contribution to the
gap at , and is due to the Zeeman energy.Comment: 5 pages, 4 figure
Quantum-Hall activation gaps in graphene
We have measured the quantum-Hall activation gaps in graphene at filling
factors and for magnetic fields up to 32 T and temperatures
from 4 K to 300 K. The gap can be described by thermal excitation to
broadened Landau levels with a width of 400 K. In contrast, the gap measured at
is strongly temperature and field dependent and approaches the expected
value for sharp Landau levels for fields T and temperatures
K. We explain this surprising behavior by a narrowing of the lowest Landau
level.Comment: 4 pages, 4 figures, updated version after review, accepted for PR
Transport and thermoelectric properties of the LaAlO/SrTiO interface
The transport and thermoelectric properties of the interface between
SrTiO and a 26-monolayer thick LaAlO-layer grown at high
oxygen-pressure have been investigated at temperatures from 4.2 K to 100 K and
in magnetic fields up to 18 T. For 4.2 K, two different electron-like
charge carriers originating from two electron channels which contribute to
transport are observed. We probe the contributions of a degenerate and a
non-degenerate band to the thermoelectric power and develop a consistent model
to describe the temperature dependence of the thermoelectric tensor. Anomalies
in the data point to an additional magnetic field dependent scattering.Comment: 7 pages, 4 figure
Scaling of the quantum-Hall plateau-plateau transition in graphene
The temperature dependence of the magneto-conductivity in graphene shows that
the widths of the longitudinal conductivity peaks, for the N=1 Landau level of
electrons and holes, display a power-law behavior following with a scaling exponent . Similarly the
maximum derivative of the quantum Hall plateau transitions
scales as with a scaling exponent
for both the first and second electron and hole Landau
level. These results confirm the universality of a critical scaling exponent.
In the zeroth Landau level, however, the width and derivative are essentially
temperature independent, which we explain by a temperature independent
intrinsic length that obscures the expected universal scaling behavior of the
zeroth Landau level
Gap opening in the zeroth Landau level of graphene
We have measured a strong increase of the low-temperature resistivity
and a zero-value plateau in the Hall conductivity at
the charge neutrality point in graphene subjected to high magnetic fields up to
30 T. We explain our results by a simple model involving a field dependent
splitting of the lowest Landau level of the order of a few Kelvin, as extracted
from activated transport measurements. The model reproduces both the increase
in and the anomalous plateau in in terms of
coexisting electrons and holes in the same spin-split zero-energy Landau level.Comment: 4 pages, 3 figure
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