10,854 research outputs found
Surprises in nonperturbative dynamics in sigma-model at finite density
The linear sigma-model occupies a unique place in
elementary particle physics and quantum field theory. It has been recently
realized that when a chemical potential for hypercharge is added, it becomes a
toy model for the description of the dynamics of the kaon condensate in high
density QCD. We review recent results in nonperturbative dynamics obtained in
the ungauged and gauged versions of this model.Comment: Brief review. 16 pages, 5 figure
Microwave Response and Spin Waves in Superconducting Ferromagnets
Excitation of spin waves is considered in a superconducting ferromagnetic
slab with the equilibrium magnetization both perpendicular and parallel to the
surface. The surface impedance is calculated and its behavior near propagation
thresholds is analyzed. Influence of non-zero magnetic induction at the surface
is considered in various cases. The results provide a basis for investigation
of materials with coexisting superconductivity and magnetism by microwave
response measurements.Comment: 10 pages, 7 figure
On an exact hydrodynamic solution for the elliptic flow
Looking for the underlying hydrodynamic mechanisms determining the elliptic
flow we show that for an expanding relativistic perfect fluid the transverse
flow may derive from a solvable hydrodynamic potential, if the entropy is
transversally conserved and the corresponding expansion "quasi-stationary",
that is mainly governed by the temperature cooling. Exact solutions for the
velocity flow coefficients and the temperature dependence of the spatial
and momentum anisotropy are obtained and shown to be in agreement with the
elliptic flow features of heavy-ion collisions.Comment: 10 pages, 4 figure
Polarons in suspended carbon nanotubes
We prove theoretically the possibility of electric-field controlled polaron
formation involving flexural (bending) modes in suspended carbon nanotubes.
Upon increasing the field, the ground state of the system with a single extra
electron undergoes a first order phase transition between an extended state and
a localized polaron state. For a common experimental setup, the threshold
electric field is only of order V/m
The effect of a velocity barrier on the ballistic transport of Dirac fermions
We propose a novel way to manipulate the transport properties of massless
Dirac fermions by using velocity barriers, defining the region in which the
Fermi velocity, , has a value that differs from the one in the
surrounding background. The idea is based on the fact that when waves travel
accross different media, there are boundary conditions that must be satisfied,
giving rise to Snell's-like laws. We find that the transmission through a
velocity barrier is highly anisotropic, and that perfect transmission always
occurs at normal incidence. When in the barrier is larger that the
velocity outside the barrier, we find that a critical transmission angle
exists, a Brewster-like angle for massless Dirac electrons.Comment: 4.3 pages, 5 figure
Edge dislocations in crystal structures considered as traveling waves of discrete models
The static stress needed to depin a 2D edge dislocation, the lower dynamic
stress needed to keep it moving, its velocity and displacement vector profile
are calculated from first principles. We use a simplified discrete model whose
far field distortion tensor decays algebraically with distance as in the usual
elasticity. An analytical description of dislocation depinning in the strongly
overdamped case (including the effect of fluctuations) is also given. A set of
parallel edge dislocations whose centers are far from each other can depin
a given one provided , where is the average inter-dislocation
distance divided by the Burgers vector of a single dislocation. Then a limiting
dislocation density can be defined and calculated in simple cases.Comment: 10 pages, 3 eps figures, Revtex 4. Final version, corrected minor
error
Unusual temperature behavior of entropy of antiferromagnetic spin state in nuclear matter with effective finite range interaction
The unusual temperature behavior of the entropy of the antiferromagnetic
(AFM) spin state in symmetric nuclear matter with the Gogny D1S interaction,
being larger at low temperatures than the entropy of nonpolarized matter, is
related to the dependence of the entropy on the effective masses of nucleons in
a spin polarized state. The corresponding conditions for comparing the
entropies of the AFM and nonpolarized states in terms of the effective masses
are formulated, including low and high temperature limits. It is shown that the
unexpected temperature behavior of the entropy of the AFM spin state at low
temperatures is caused by the violation of the corresponding low temperature
criterium.Comment: version accepted for publication in PR
Absorption suppression in photonic crystals
We study electromagnetic properties of periodic composite structures, such as
photonic crystals, involving lossy components. We show that in many cases a
properly designed periodic structure can dramatically suppress the losses
associated with the absorptive component, while preserving or even enhancing
its useful functionality. As an example, we consider magnetic photonic
crystals, in which the lossy magnetic component provides nonreciprocal Faraday
rotation. We show that the electromagnetic losses in the composite structure
can be reduced by up to two orders of magnitude, compared to those of the
uniform magnetic sample made of the same lossy magnetic material. Importantly,
the dramatic absorption reduction is not a resonance effect and occurs over a
broad frequency range covering a significant portion of photonic frequency
band
Multiphoton antiresonance in large-spin systems
We study nonlinear response of a spin with easy-axis anisotropy. The
response displays sharp dips or peaks when the modulation frequency is
adiabatically swept through multiphoton resonance. The effect is a consequence
of a special symmetry of the spin dynamics in a magnetic field for the
anisotropy energy . The occurrence of the dips or peaks is
determined by the spin state. Their shape strongly depends on the modulation
amplitude. Higher-order anisotropy breaks the symmetry, leading to sharp steps
in the response as function of frequency. The results bear on the dynamics of
molecular magnets in a static magnetic field.Comment: Submitted to PR
Low energy excitations and singular contributions in the thermodynamics of clean Fermi liquids
Using a recently suggested method of bosonization in an arbitrary dimension,
we study the anomalous contribution of the low energy spin and charge
excitations to thermodynamic quantities of a two-dimensional (2D) Fermi liquid.
The method is slightly modified for the present purpose such that the effective
supersymmetric action no longer contains the high energy degrees of freedom but
still accounts for effects of the finite curvature of the Fermi surface.
Calculating the anomalous contribution to the specific heat, we
show that the leading logarithmic in temperature corrections to can be obtained in a scheme combining a summation of ladder diagrams
and renormalization group equations. The final result is represented as the sum
of two separate terms that can be interpreted as coming from singlet and
triplet superconducting excitations. The latter may diverge in certain regions
of the coupling constants, which should correspond to the formation of triplet
Cooper pairs.Comment: 29 pages, 13 figure
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