12,047 research outputs found
Chiral Anomaly and Classical Negative Magnetoresistance of Weyl Metals
We consider the classical magnetoresistance of a Weyl metal in which the
electron Fermi surface possess nonzero fluxes of the Berry curvature. Such a
system may exhibit large negative magnetoresistance with unusual anisotropy as
a function of the angle between the electric and magnetic fields. In this case
the system can support a new type of plasma waves. These phenomena are
consequences of chiral anomaly in electron transport theory.Comment: 4 pages, 2 figure
Charged and superconducting vortices in dense quark matter
Quark matter at astrophysical densities may contain stable vortices due to
the spontaneous breaking of hypercharge symmetry by kaon condensation. We argue
that these vortices could be both charged and electrically superconducting.
Current carrying loops (vortons) could be long lived and play a role in the
magnetic and transport properties of this matter. We provide a scenario for
vorton formation in protoneutron stars.Comment: Replaced with the published version. A typographical error in Eq. 2
is correcte
Clustering of vacancy defects in high-purity semi-insulating SiC
Positron lifetime spectroscopy was used to study native vacancy defects in
semi-insulating silicon carbide. The material is shown to contain (i) vacancy
clusters consisting of 4--5 missing atoms and (ii) Si vacancy related
negatively charged defects. The total open volume bound to the clusters
anticorrelates with the electrical resistivity both in as-grown and annealed
material. Our results suggest that Si vacancy related complexes compensate
electrically the as-grown material, but migrate to increase the size of the
clusters during annealing, leading to loss of resistivity.Comment: 8 pages, 5 figure
Pion Propagation near the QCD Chiral Phase Transition
We point out that, in analogy with spin waves in antiferromagnets, all
parameters describing the real-time propagation of soft pions at temperatures
below the QCD chiral phase transition can be expressed in terms of static
correlators. This allows, in principle, the determination of the soft pion
dispersion relation on the lattice. Using scaling and universality arguments,
we determine the critical behavior of the parameters of pion propagation. We
predict that when the critical temperature is approached from below, the pole
mass of the pion drops despite the growth of the pion screening mass. This fact
is attributed to the decrease of the pion velocity near the phase transition.Comment: 8 pages (single column), RevTeX; added references, version to be
published in PR
QCD-like Theories at Finite Baryon and Isospin Density
We use 2-color QCD as a model to study the effects of simultaneous presence
of chemical potentials for isospin charge, , and for baryon number,
. We determine the phase diagrams for 2 and 4 flavor theories using the
method of effective chiral Lagrangians at low densities and weak coupling
perturbation theory at high densities. We determine the values of various
condensates and densities as well as the spectrum of excitations as functions
of and . A similar analysis of QCD with quarks in the adjoint
representation is also presented. Our results can be of relevance for lattice
simulations of these theories. We predict a phase of inhomogeneous condensation
(Fulde-Ferrel-Larkin-Ovchinnikov phase) in the 2 colour 2 flavor theory, while
we do not expect it the 4 flavor case or in other realizations of QCD with a
positive measure.Comment: 17 pages, 14 figure
Real-time pion propagation in finite-temperature QCD
We argue that in QCD near the chiral limit, at all temperatures below the
chiral phase transition, the dispersion relation of soft pions can be expressed
entirely in terms of three temperature-dependent quantities: the pion screening
mass, a pion decay constant, and the axial isospin susceptibility. The
definitions of these quantities are given in terms of equal-time (static)
correlation functions. Thus, all three quantities can be determined directly by
lattice methods. The precise meaning of the Gell-Mann--Oakes--Renner relation
at finite temperature is given.Comment: 25 pages, 2 figures; v2: discussion on the region of applicability
expanded, to be published in PR
Linear Confinement and AdS/QCD
In a theory with linear confinement, such as QCD, the masses squared m^2 of
mesons with high spin S or high radial excitation number n are expected, from
semiclassical arguments, to grow linearly with S and n. We show that this
behavior can be reproduced within a putative 5-dimensional theory
holographically dual to QCD (AdS/QCD). With the assumption that such a dual
theory exists and describes highly excited mesons as well, we show that
asymptotically linear m^2 spectrum translates into a strong constraint on the
INFRARED behavior of that theory. In the simplest model which obeys such a
constraint we find m^2 ~ (n+S).Comment: 14 pages, 1 figur
Asymptotic deconfinement in high-density QCD
We discuss QCD with two light flavors at large baryon chemical potential mu.
Color superconductivity leads to partial breaking of the color SU(3) group. We
show that the infrared physics is governed by the gluodynamics of the remaining
SU(2) group with an exponentially soft confinement scale Lambda_QCD'
Delta*exp[-a*mu/(g*Delta)], where Delta<<mu is the superconducting gap, g is
the strong coupling, and a=0.81... We estimate that at moderate baryon
densities Lambda_QCD' is O(10 MeV) or smaller. The confinement radius increases
exponentially with density, leading to "asymptotic deconfinement." The velocity
of the SU(2) gluons is small due to the large dielectric constant of the
medium.Comment: 4 pages; restructured, published versio
QCD at finite isospin density
QCD at finite isospin chemical potential mu_I has no fermion sign problem and
can be studied on the lattice. We solve this theory analytically in two limits:
at low mu_I where chiral perturbation theory is applicable, and at
asymptotically high mu_I where perturbative QCD works. At low isospin density
the ground state is a pion condensate, whereas at high density it is a Fermi
liquid with Cooper pairing. The pairs carry the same quantum numbers as the
pion. This leads us to a conjecture that the transition from hadron to quark
matter is smooth, which passes several tests. Our results imply a nontrivial
phase diagram in the space of temperature and chemical potentials of isospin
and baryon number.Comment: 4 pages, 1 figure, version to appear in PR
Combined electrical transport and capacitance spectroscopy of a field effect transistor
We have measured both the current-voltage (-)
and capacitance-voltage (-) characteristics of a
field effect transistor. From the measured capacitance
we calculate the electron surface density and show that its gate voltage
dependence follows the theoretical prediction resulting from the
two-dimensional free electron model. This model allows us to fit the measured
- characteristics over the \emph{entire range} of
. Combining this experimental result with the measured
current-voltage characteristics, we determine the field effect mobility as a
function of gate voltage. We show that for our device this improved combined
approach yields significantly smaller values (more than a factor of 4) of the
electron mobility than the conventional analysis of the current-voltage
characteristics only.Comment: to appear in Applied Physics Letter
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