201 research outputs found
Anisotropic magnetoresistance in a 2DEG in a quasi-random magnetic field
We present magnetotransport results for a 2D electron gas (2DEG) subject to
the quasi-random magnetic field produced by randomly positioned sub-micron Co
dots deposited onto the surface of a GaAs/AlGaAs heterostructure. We observe
strong local and non-local anisotropic magnetoresistance for external magnetic
fields in the plane of the 2DEG. Monte-Carlo calculations confirm that this is
due to the changing topology of the quasi-random magnetic field in which
electrons are guided predominantly along contours of zero magnetic field.Comment: 4 pages, 6 figures, submitted to Phys. Rev.
Optically opaque color-flavor locked phase inside compact stars
The contribution of thermally excited electron-positron pairs to the bulk
properties of the color-flavor locked quark phase inside compact stars is
examined. The presence of these pairs causes the photon mean free path to be
much smaller than a typical core radius ( km) for all
temperatures above 25 keV so that the photon contribution to the thermal
conductivity is much smaller than that of the Nambu-Goldstone bosons. We also
find that the electrons and positrons dominate the electrical conductivity,
while their contributions to the total thermal energy is negligible.Comment: 3 pages, 2 figures. Published versio
Absence of lattice strain anomalies at the electronic topological transition in zinc at high pressure
High pressure structural distortions of the hexagonal close packed (hcp)
element zinc have been a subject of controversy. Earlier experimental results
and theory showed a large anomaly in lattice strain with compression in zinc at
about 10 GPa which was explained theoretically by a change in Fermi surface
topology. Later hydrostatic experiments showed no such anomaly, resulting in a
discrepancy between theory and experiment. We have computed the compression and
lattice strain of hcp zinc over a wide range of compressions using the
linearized augmented plane wave (LAPW) method paying special attention to
k-point convergence. We find that the behavior of the lattice strain is
strongly dependent on k-point sampling, and with large k-point sets the
previously computed anomaly in lattice parameters under compression disappears,
in agreement with recent experiments.Comment: 9 pages, 6 figures, Phys. Rev. B (in press
Breached Pairing Superfluidity at Finite Temperature and Density
A general analysis on Fermion pairing at finite temperature and density
between different species with mismatched Fermi surfaces is presented. Very
different from the temperature effect of BCS phase, the recently found breached
pairing phase resulted from density difference of the two species lies in a
region with calabash-like shape in the plane, and the most probable
temperature for the new phase's creation is finite but not zero.Comment: 5 papes, 5 figures. Comments are welcome to
[email protected]
Warm stellar matter with deconfinement: application to compact stars
We investigate the properties of mixed stars formed by hadronic and quark
matter in -equilibrium described by appropriate equations of state (EOS)
in the framework of relativistic mean-field theory. We use the non- linear
Walecka model for the hadron matter and the MIT Bag and the Nambu-Jona-Lasinio
models for the quark matter. The phase transition to a deconfined quark phase
is investigated. In particular, we study the dependence of the onset of a mixed
phase and a pure quark phase on the hyperon couplings, quark model and
properties of the hadronic model. We calculate the strangeness fraction with
baryonic density for the different EOS. With the NJL model the strangeness
content in the mixed phase decreases. The calculations were performed for T=0
and for finite temperatures in order to describe neutron and proto-neutron
stars. The star properties are discussed. Both the Bag model and the NJL model
predict a mixed phase in the interior of the star. Maximum allowed masses for
proto-neutron stars are larger for the NJL model ( M)
than for the Bag model ( M).Comment: RevTeX,14 figures, accepted to publication in Physical Review
Spin-one color superconductivity in compact stars?- an analysis within NJL-type models
We present results of a microscopic calculation using NJL-type model of
possible spin-one pairings in two flavor quark matter for applications in
compact star phenomenology. We focus on the color-spin locking phase (CSL) in
which all quarks pair in a symmetric way, in which color and spin states are
locked. The CSL condensate is particularly interesting for compact star
applications since it is flavor symmetric and could easily satisfy charge
neutrality. Moreover, the fact that in this phase all quarks are gapped might
help to suppress the direct Urca process, consistent with cooling models. The
order of magnitude of these small gaps (~1 MeV) will not influence the EoS, but
their also small critical temperatures (T_c ~800 keV) could be relevant in the
late stages neutron star evolution, when the temperature falls below this value
and a CSL quark core could form.Comment: 7 pages, 7 figures, revised version, accepted for the Conference
Proceedings of "Isolated Neutron Stars: from the Interior to the Surface",
London, 24-28. April 200
A calculation of the QCD phase diagram at finite temperature, and baryon and isospin chemical potentials
We study the phases of a two-flavor Nambu-Jona-Lasinio model at finite
temperature , baryon and isospin chemical potentials:
, . This study
completes a previous analysis where only small isospin chemical potentials
were consideredComment: 21 pages, 13 figures included, two more refernces adde
Chiral symmetry breaking, color superconductivity and color neutral quark matter: a variational approach
We investigate the vacuum realignment for chiral symmetry breaking and color
superconductivity at finite density in Nambu-Jona-Lasinio model in a
variational method. The treatment allows us to investigate simultaneous
formation of condensates in quark antiquark as well as in diquark channels. The
methodology involves an explicit construction of a variational ground state and
minimisation of the thermodynamic potential. Color and electric charge
neutrality conditions are imposed through introduction of appropriate chemical
potentials. Color and flavor dependent condensate functions are determined
through minimisation of the thermodynamic potential. The equation of state is
calculated. Simultaneous existence of a mass gap and superconducting gap is
seen in a small window of quark chemical potential within the model when charge
neutrality conditions are not imposed. Enforcing color and electric charge
neutrality conditions gives rise to existence of gapless superconducting modes
depending upon the magnitude of the gap and the difference of the chemical
potentials of the condensing quarks.Comment: 13 pages, 6 figures,to appear in Phys. Rev.
Frustration and the Kondo effect in heavy fermion materials
The observation of a separation between the antiferromagnetic phase boundary
and the small-large Fermi surface transition in recent experiments has led to
the proposal that frustration is an important additional tuning parameter in
the Kondo lattice model of heavy fermion materials. The introduction of a Kondo
(K) and a frustration (Q) axis into the phase diagram permits us to discuss the
physics of heavy fermion materials in a broader perspective. The current
experimental situation is analysed in the context of this combined "QK" phase
diagram. We discuss various theoretical models for the frustrated Kondo
lattice, using general arguments to characterize the nature of the -electron
localization transition that occurs between the spin liquid and heavy Fermi
liquid ground-states. We concentrate in particular on the Shastry--Sutherland
Kondo lattice model, for which we establish the qualitative phase diagram using
strong coupling arguments and the large- expansion. The paper closes with
some brief remarks on promising future theoretical directions.Comment: To appear in a special issue of JLT
Two lectures on color superconductivity
The first lecture provides an introduction to the physics of color
superconductivity in cold dense quark matter. The main color superconducting
phases are briefly described and their properties are listed. The second
lecture covers recent developments in studies of color superconducting phases
in neutral and beta-equilibrated matter. The properties of gapless color
superconducting phases are discussed.Comment: 56 pages, 9 figures. Minor corrections and references added. Lectures
delivered at the IARD 2004 conference, Saas Fee, Switzerland, June 12 - 19,
2004, and at the Helmholtz International Summer School and Workshop on Hot
points in Astrophysics and Cosmology, JINR, Dubna, Russia, August 2 - 13,
200
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