6,201 research outputs found
Theory of the Nernst effect near quantum phase transitions in condensed matter, and in dyonic black holes
We present a general hydrodynamic theory of transport in the vicinity of
superfluid-insulator transitions in two spatial dimensions described by
"Lorentz"-invariant quantum critical points. We allow for a weak impurity
scattering rate, a magnetic field B, and a deviation in the density, \rho, from
that of the insulator. We show that the frequency-dependent thermal and
electric linear response functions, including the Nernst coefficient, are fully
determined by a single transport coefficient (a universal electrical
conductivity), the impurity scattering rate, and a few thermodynamic state
variables. With reasonable estimates for the parameters, our results predict a
magnetic field and temperature dependence of the Nernst signal which resembles
measurements in the cuprates, including the overall magnitude. Our theory
predicts a "hydrodynamic cyclotron mode" which could be observable in ultrapure
samples. We also present exact results for the zero frequency transport
co-efficients of a supersymmetric conformal field theory (CFT), which is
solvable by the AdS/CFT correspondence. This correspondence maps the \rho and B
perturbations of the 2+1 dimensional CFT to electric and magnetic charges of a
black hole in the 3+1 dimensional anti-de Sitter space. These exact results are
found to be in full agreement with the general predictions of our hydrodynamic
analysis in the appropriate limiting regime. The mapping of the hydrodynamic
and AdS/CFT results under particle-vortex duality is also described.Comment: 44 pages, 4 figures; (v3) Added new subsection highlighting negative
Hall resistance at hole densities smaller than 1/
Oscillations of the Nernst coefficient in bismuth
We calculate the magnetic-field dependence (oscillations) of the Nernst
coefficient in bismuth at low temperatures for the case when the magnetic field
is directed along the trigonal axis of the crystal. In the calculations we take
into account the scattering of the electrons and holes in bismuth on impurities
and the dependence of this scattering on the magnetic field. The results of
these calculations are compared with the experimental data recently published
Nernst-Ettingshausen effect in two-component electronic liquids
A simple model describing the Nernst-Ettingshausen effect (NEE) in
two-component electronic liquids is formulated. The examples considered include
graphite, where the normal and Dirac fermions coexist, superconductor in
fluctuating regime, with coexisting Cooper pairs and normal electrons, and the
inter-stellar plasma of electrons and protons. We give a general expression for
the Nernst constant and show that the origin of a giant NEE is in the strong
dependence of the chemical potential on temperature in all cases
Thermohydrodynamics in Quantum Hall Systems
A theory of thermohydrodynamics in two-dimensional electron systems in
quantizing magnetic fields is developed including a nonlinear transport regime.
Spatio-temporal variations of the electron temperature and the chemical
potential in the local equilibrium are described by the equations of
conservation with the number and thermal-energy flux densities. A model of
these flux densities due to hopping and drift processes is introduced for a
random potential varying slowly compared to both the magnetic length and the
phase coherence length. The flux measured in the standard transport experiment
is derived and is used to define a transport component of the flux density. The
equations of conservation can be written in terms of the transport component
only. As an illustration, the theory is applied to the Ettingshausen effect, in
which a one-dimensional spatial variation of the electron temperature is
produced perpendicular to the current.Comment: 10 pages, 1 figur
Measurement of the decay form factors in the OKA experiment
A precise measurement of the vector and axial-vector form factors difference
in the decay is presented.
About 95K events of are selected in
the OKA experiment. The result is .
Both errors are smaller than in the previous measurements.Comment: 9 pages, 8 figure
Quasiparticle Hall Transport of d-wave Superconductors in Vortex State
We present a theory of quasiparticle Hall transport in strongly type-II
superconductors within their vortex state. We establish the existence of
integer quantum spin Hall effect in clean unconventional
superconductors in the vortex state from a general analysis of the
Bogoliubov-de Gennes equation. The spin Hall conductivity is
shown to be quantized in units of . This result does not
rest on linearization of the BdG equations around Dirac nodes and therefore
includes inter-nodal physics in its entirety. In addition, this result holds
for a generic inversion-symmetric lattice of vortices as long as the magnetic
field satisfies . We then derive the
Wiedemann-Franz law for the spin and thermal Hall conductivity in the vortex
state. In the limit of , the thermal Hall conductivity satisfies
. The
transitions between different quantized values of as well as
relation to conventional superconductors are discussed.Comment: 18 pages REVTex, 3 figures, references adde
Experimental study of direct photon emission in K- --> pi- pi0 gamma decay using ISTRA+ detector
The branching ratio in the charged-pion kinetic energy region of 55 to 90 MeV
for the direct photon emission in the K- --> pi- pi0 gamma decay has been
measured using in-flight decays detected with the ISTRA+ setup operating in the
25 GeV/c negative secondary beam of the U-70 PS. The value
Br(DE)=[0.37+-0.39(stat)+-0.10(syst)]*10^(-5) obtained from the analysis of 930
completely reconstructed events is consistent with the average value of two
stopped-kaon experiments, but it differs by 2.5 standard deviations from the
average value of three in-flight-kaon experiments. The result is also compared
with recent theoretical predictions.Comment: 13 pages, 8 figure
Effective electro-optical modulation with high extinction ratio by a graphene-silicon microring resonator
Graphene opens up for novel optoelectronic applications thanks to its high
carrier mobility, ultra-large absorption bandwidth, and extremely fast material
response. In particular, the opportunity to control optoelectronic properties
through tuning of Fermi level enables electro-optical modulation,
optical-optical switching, and other optoelectronics applications. However,
achieving a high modulation depth remains a challenge because of the modest
graphene-light interaction in the graphene-silicon devices, typically,
utilizing only a monolayer or few layers of graphene. Here, we comprehensively
study the interaction between graphene and a microring resonator, and its
influence on the optical modulation depth. We demonstrate graphene-silicon
microring devices showing a high modulation depth of 12.5 dB with a relatively
low bias voltage of 8.8 V. On-off electro-optical switching with an extinction
ratio of 3.8 dB is successfully demonstrated by applying a square-waveform with
a 4 V peak-to-peak voltage.Comment: 12 pages, including 7 figure
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