11,843 research outputs found
Evaluation of specific heat for superfluid helium between 0 - 2.1 K based on nonlinear theory
The specific heat of liquid helium was calculated theoretically in the Landau
theory. The results deviate from experimental data in the temperature region of
1.3 - 2.1 K. Many theorists subsequently improved the results of the Landau
theory by applying temperature dependence of the elementary excitation energy.
As well known, many-body system has a total energy of Galilean covariant form.
Therefore, the total energy of liquid helium has a nonlinear form for the
number distribution function. The function form can be determined using the
excitation energy at zero temperature and the latent heat per helium atom at
zero temperature. The nonlinear form produces new temperature dependence for
the excitation energy from Bose condensate. We evaluate the specific heat using
iteration method. The calculation results of the second iteration show good
agreement with the experimental data in the temperature region of 0 - 2.1 K,
where we have only used the elementary excitation energy at 1.1 K.Comment: 6 pages, 3 figures, submitted to Journal of Physics: Conference
Serie
The phase structure of a chiral model with dilatons in hot and dense matter
We explore the phase structure of a chiral model of constituent quarks and
gluons implementing scale symmetry breaking at finite temperature and chemical
potential. In this model the chiral dynamics is intimately linked to the trace
anomaly saturated by a dilaton field. The thermodynamics is governed by two
condensates, thermal expectation values of sigma and dilaton fields, which are
the order parameters responsible for the phase transitions associated with the
chiral and scale symmetries. Within the mean field approximation, we find that
increasing temperature a system experiences a chiral phase transition and then
a first-order phase transition of partial scale symmetry restoration
characterized by a melting gluon-condensate takes place at a higher
temperature. There exists a region at finite chemical potential where the scale
symmetry remains dynamically broken while the chiral symmetry is restored. We
also give a brief discussion on the sigma-meson mass constrained from Lattice
QCD.Comment: 6 pages, 5 figures; v2) new figures and references adde
The corrections to the first moment of the polarized virtual photon structure function
We present the next-to-next-to-leading order () corrections
to the first moment of the polarized virtual photon structure function
in the kinematical region ,
where is the mass squared of the probe (target) photon and
is the QCD scale parameter. In order to evaluate the three-loop-level
photon matrix element of the flavor singlet axial current, we resort to the
Adler-Bardeen theorem for the axial anomaly and we calculate in effect the
two-loop diagrams for the photon matrix element of the gluon operator. The
corrections are found to be about 3% of the sum of the
leading order () andthe next-to-leading order ()
contributions, when and , and the
number of active quark flavors is three to five.Comment: 21 page
Ultrafast Spin Dynamics in GaAs/GaSb/InAs Heterostructures Probed by Second Harmonic Generation
We report the first application of pump-probe second harmonic generation
(SHG) measurements to characterize optically-induced magnetization in
non-magnetic multilayer semiconductors. In the experiment, coherent spins are
selectively excited by a pump beam in the GaAs layer of GaAs/GaSb/InAs
structures. However, the resulting net magnetization manifests itself through
the induced SHG probe signal from the GaSb/InAs interface, thus indicating a
coherent spin transport across the heterostructure. We find that the
magnetization dynamics is governed by an interplay between the spin density
evolution at the interfaces and the spin dephasing.Comment: 4 pages + 4 Fig
Are black holes over-produced during preheating?
We provide a simple but robust argument that primordial black hole (PBH)
production generically does {\em not} exceed astrophysical bounds during the
resonant preheating phase after inflation. This conclusion is supported by
fully nonlinear lattice simulations of various models in two and three
dimensions which include rescattering but neglect metric perturbations. We
examine the degree to which preheating amplifies density perturbations at the
Hubble scale and show that at the end of the parametric resonance, power
spectra are universal, with no memory of the power spectrum at the end of
inflation. In addition we show how the probability distribution of density
perturbations changes from exponential on very small scales to Gaussian when
smoothed over the Hubble scale -- the crucial length for studies of primordial
black hole formation -- hence justifying the standard assumption of
Gaussianity.Comment: 12 pages, 8 figures, revtex, added references for section
Ultrafast Dynamics of Interfacial Electric Fields in Semiconductor Heterostructures Monitored by Pump-Probe Second Harmonic Generation
We report first measurements of the ultrafast dynamics of interfacial
electric fields in semiconductor multilayers using pump-probe second harmonic
generation (SHG). A pump beam was tuned to excite carriers in all layers of
GaAs/GaSb and GaAs/GaSb/InAs heterostructures. Further carrier dynamics
manifests itself via electric fields created by by charge separation at
interfaces. The evolution of interfacial fields is monitored by a probe beam
through the eletric-field-induced SHG signal. We distinguish between several
stages of dynamics originating from redistribution of carriers between the
layers. We also find a strong enhancement of the induced electric field caused
by hybridization of the conduction and valence bands at the GaSb/InAs
interface.Comment: 4 pages + 2 fig
Theory of superconductivity of carbon nanotubes and graphene
We present a new mechanism of carbon nanotube superconductivity that
originates from edge states which are specific to graphene. Using on-site and
boundary deformation potentials which do not cause bulk superconductivity, we
obtain an appreciable transition temperature for the edge state. As a
consequence, a metallic zigzag carbon nanotube having open boundaries can be
regarded as a natural superconductor/normal metal/superconductor junction
system, in which superconducting states are developed locally at both ends of
the nanotube and a normal metal exists in the middle. In this case, a signal of
the edge state superconductivity appears as the Josephson current which is
sensitive to the length of a nanotube and the position of the Fermi energy.
Such a dependence distinguishs edge state superconductivity from bulk
superconductivity.Comment: 5 pages, 2 figure
Magnetic Properties of 2-Dimensional Dipolar Squares: Boundary Geometry Dependence
By means of the molecular dynamics simulation on gradual cooling processes,
we investigate magnetic properties of classical spin systems only with the
magnetic dipole-dipole interaction, which we call dipolar systems. Focusing on
their finite-size effect, particularly their boundary geometry dependence, we
study two finite dipolar squares cut out from a square lattice with
and , where is an angle between the direction of the lattice axis
and that of the square boundary. Distinctly different results are obtained in
the two dipolar squares. In the square, the ``from-edge-to-interior
freezing'' of spins is observed. Its ground state has a multi-domain structure
whose domains consist of the two among infinitely (continuously) degenerated
Luttinger-Tisza (LT) ground-state orders on a bulk square lattice, i.e., the
two antiferromagnetically aligned ferromagnetic chains (af-FMC) orders directed
in parallel to the two lattice axes. In the square, on the other
hand, the freezing starts from the interior of the square, and its ground state
is nearly in a single domain with one of the two af-FMC orders. These geometry
effects are argued to originate from the anisotropic nature of the
dipole-dipole interaction which depends on the relative direction of sites in a
real space of the interacting spins.Comment: 21 pages, 13 figures, submitted to Journal of Physical Society Japa
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