388 research outputs found
Detecting D-Wave Pairing and Collective Modes in Fermionic Condensates with Bragg Scattering
We show how the appearance of d-wave pairing in fermionic condensates
manifests itself in inelastic light scattering. Specifically, we calculate the
Bragg scattering intensity from the dynamic structure factor and the spin
susceptibility, which can be inferred from spin flip Raman transitions. This
information provides a precise tool with which we can identify nontrivial
correlations in the state of the system beyond the information contained in the
density profile imaging alone. Due to the lack of Coulomb effects in neutral
superfluids, this is also an opportunity to observe the Anderson-Bogoliubov
collective mode
Interlayer tunneling spectroscopy of graphite at high magnetic field oriented parallel to the layers
Interlayer tunneling in graphite mesa-type structures is studied at a strong
in-plane magnetic field up to 55 T and low temperature K. The
tunneling spectrum vs. has a pronounced peak at a finite voltage
. The peak position increases linearly with . To explain the
experiment, we develop a theoretical model of graphite in the crossed electric
and magnetic fields. When the fields satisfy the resonant condition
, where is the velocity of the two-dimensional Dirac electrons in
graphene, the wave functions delocalize and give rise to the peak in the
tunneling spectrum observed in the experiment.Comment: 6 pages, 6 figures; corresponds to the published version in Eur.
Phys. J. Special Topics, Proceedings of the IMPACT conference 2012,
http://lptms.u-psud.fr/impact2012
Field-induced spin density wave in (TMTSF)NO
Interlayer magnetoresistance of the Bechgaard salt (TMTSF)NO is
investigated up to 50 teslas under pressures of a few kilobars. This compound,
the Fermi surface of which is quasi two-dimensional at low temperature, is a
semi metal under pressure. Nevertheless, a field-induced spin density wave is
evidenced at 8.5 kbar above 20 T. This state is characterized by a
drastically different spectrum of the quantum oscillations compared to the low
pressure spin density wave state.Comment: to be published in Phys. Rev. B 71 (2005
Deconfined Fermions but Confined Coherence?
The cuprate superconductors and certain organic conductors exhibit transport
which is qualitatively anisotropic, yet at the same time other properties of
these materials strongly suggest the existence of a Fermi surface and low
energy excitations with substantial free electron character. The former of
these features is very difficult to account for if the material possesses three
dimensional coherence, while the latter is inconsistent with a description
based on a two dimensional fixed point. We therefore present a new proposal for
these materials in which they are categorized by a fixed point at which
transport in one direction is not renormalization group irrelevant, but is
intrinsically incoherent, i.e. the incoherence is present in a pure system, at
zero temperature. The defining property of such a state is that single electron
coherence is confined to lower dimensional subspaces (planes or chains) so that
it is impossible to observe interference effects between histories which
involve electrons moving between these subspaces.Comment: 31 pages, REVTEX, 3 eps figures, epsf.tex macr
Sign reversals of the quantum Hall effect and helicoidal magnetic-field-induced spin-density waves in quasi-one-dimensional organic conductors
We study the effect of umklapp scattering on the magnetic-field-induced
spin-density-wave phases, which are experimentally observed in the
quasi-one-dimensional organic conductors of the Bechgaard salts family. Within
the framework of the quantized nesting model, we show that umklapp processes
may naturally explain sign reversals of the quantum Hall effect (QHE) observed
in these conductors. Moreover, umklapp scattering can change the polarization
of the spin-density wave (SDW) from linear (sinusoidal SDW) to circular
(helicoidal SDW). The QHE vanishes in the helicoidal phases, but a
magnetoelectric effect appears. These two characteristic properties may be
utilized to detect the magnetic-field-induced helicoidal SDW phases
experimentally.Comment: 4 pages, latex, 3 figure
Quantum Hall effect anomaly and collective modes in the magnetic-field-induced spin-density-wave phases of quasi-one-dimensional conductors
We study the collective modes in the magnetic-field-induced spin-density-wave
(FISDW) phases experimentally observed in organic conductors of the Bechgaard
salts family. In phases that exhibit a sign reversal of the quantum Hall effect
(Ribault anomaly), the coexistence of two spin-density waves gives rise to
additional collective modes besides the Goldstone modes due to spontaneous
translation and rotation symmetry breaking. These modes strongly affect the
charge and spin response functions. We discuss some experimental consequences
for the Bechgaard salts.Comment: Final version (LaTex, 8 pages, no figure), to be published in
Europhys. Let
Порівняльний аналіз лінійного та нелінійного правил сумішей при моделюванні напруженого стану півпростору
In the present work we solve the axially symmetric problem of a half-space under thermal loading. The statement of the problem includes: Cauchy relations, equations of motion, heat conduction equation, initial conditions, thermal and mechanical boundary conditions. The thermomechanical behavior of an isotropic material is described by the Bodner–Partom unified model of flow generalized in the case of microstructure influence on inelastic characteristics of steel. To determine the parameters of the model corresponded to yield stress and yield strength the mixture rule is utilized. The problem is solved with using the finite element technique. The numerical realization of our problem is performed with the help of step-by-step time integration. Equations of the evolution for the inelastic flow model are integrated by the second-order Euler implicit method. The equations of motion are integrated by the Newmark method, whereas the heat-conduction equation is integrated by the first-order implicit method. We use quadrangular isoparametric elements. The parameters of a fine grid are chosen with the help of the criterion of practical convergence of the solutions. The stress state taking into account linear and nonlinear rules of mixtures is described.
Pages of the article in the issue: 94 - 97
Language of the article: UkrainianУ даній статті чисельно досліджується осесиметрична задача про термічне імпульсне навантаження півпростору. Постановка задачі включає співвідношення Коші, рівняння руху, рівняння теплопровідності, початкові умови, теплові та механічні граничні умови. Для моделювання механічної поведінки матеріалу використовується модель течії Боднера-Партома, узагальнена на випадок впливу мікроструктури на непружні характеристики сталі. Для визначення параметрів моделі, що відповідають за границю текучості та тимчасовий опір матеріалу, використано лінійне правило сумішей. Задача розв’язується за допомогою скінченно-елементної методики. Чисельна реалізація задачі проводиться за допомогою покрокового інтегрування за часом. Описано напружений стан півпростору при врахуванні лінійного та нелінійного правил сумішей
Directed Random Markets: Connectivity determines Money
Boltzmann-Gibbs distribution arises as the statistical equilibrium
probability distribution of money among the agents of a closed economic system
where random and undirected exchanges are allowed. When considering a model
with uniform savings in the exchanges, the final distribution is close to the
gamma family. In this work, we implement these exchange rules on networks and
we find that these stationary probability distributions are robust and they are
not affected by the topology of the underlying network. We introduce a new
family of interactions: random but directed ones. In this case, it is found the
topology to be determinant and the mean money per economic agent is related to
the degree of the node representing the agent in the network. The relation
between the mean money per economic agent and its degree is shown to be linear.Comment: 14 pages, 6 figure
Collective modes in a system with two spin-density waves: the `Ribault' phase of quasi-one-dimensional organic conductors
We study the long-wavelength collective modes in the magnetic-field-induced
spin-density-wave (FISDW) phases experimentally observed in organic conductors
of the Bechgaard salts family, focusing on phases that exhibit a sign reversal
of the quantum Hall effect (Ribault anomaly). We have recently proposed that
two SDW's coexist in the Ribault phase, as a result of Umklapp processes. When
the latter are strong enough, the two SDW's become circularly polarized
(helicoidal SDW's). In this paper, we study the collective modes which result
from the presence of two SDW's. We find two Goldstone modes, an out-of-phase
sliding mode and an in-phase spin-wave mode, and two gapped modes. The sliding
Goldstone mode carries only a fraction of the total optical spectral weight,
which is determined by the ratio of the amplitude of the two SDW's. In the
helicoidal phase, all the spectral weight is pushed up above the SDW gap. We
also point out similarities with phase modes in two-band or bilayer
superconductors. We expect our conclusions to hold for generic two-SDW systems.Comment: Revised version, 25 pages, RevTex, 7 figure
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