42,268 research outputs found
A controlled expansion for certain non-Fermi liquid metals
The destruction of Fermi liquid behavior when a gapless Fermi surface is
coupled to a fluctuating gapless boson field is studied theoretically. This
problem arises in a number of different contexts in quantum many body physics.
Examples include fermions coupled to a fluctuating transverse gauge field
pertinent to quantum spin liquid Mott insulators, and quantum critical metals
near a Pomeranchuk transition. We develop a new controlled theoretical approach
to determining the low energy physics. Our approach relies on combining an
expansion in the inverse number (N) of fermion species with a further expansion
in the parameter \epsilon = z_b -2 where z_b is the dynamical critical exponent
of the boson field. We show how this limit allows a systematic calculation of
the universal low energy physics of these problems. The method is illustrated
by studying spinon fermi surface spin liquids, and a quantum critical metal at
a second order electronic nematic phase transition. We calculate the low energy
single particle spectra, and various interesting two particle correlation
functions. In some cases deviations from the popular Random Phase Approximation
results are found. Some of the same universal singularities are also calculated
to leading non-vanishing order using a perturbative renormalization group
calculation at small N extending previous results of Nayak and Wilczek.
Implications for quantum spin liquids, and for Pomeranchuk transitions are
discussed. For quantum critical metals at a nematic transition we show that the
tunneling density of states has a power law suppression at low energies.Comment: 19 pages, 15 figure
A Comparative Study of the Parker Instability under Three Models of the Galactic Gravity
To examine how non-uniform nature of the Galactic gravity might affect length
and time scales of the Parker instability, we took three models of gravity,
uniform, linear and realistic ones. To make comparisons of the three gravity
models on a common basis, we first fixed the ratio of magnetic pressure to gas
pressure at = 0.25, that of cosmic-ray pressure at = 0.4, and
the rms velocity of interstellar clouds at = 6.4 km s, and then
adjusted parameters of the gravity models in such a way that the resulting
density scale heights for the three models may all have the same value of 160
pc. Performing linear stability analyses onto equilibrium states under the
three models with the typical ISM conditions, we calculate the maximum growth
rate and corresponding length scale for each of the gravity models. Under the
uniform gravity the Parker instability has the growth time of 1.2
years and the length scale of 1.6 kpc for symmetric mode. Under the realistic
gravity it grows in 1.8 years for both symmetric and
antisymmetric modes, and develops density condensations at intervals of 400 pc
for the symmetric mode and 200 pc for the antisymmetric one. A simple change of
the gravity model has thus reduced the growth time by almost an order of
magnitude and its length scale by factors of four to eight. These results
suggest that an onset of the Parker instability in the ISM may not necessarily
be confined to the regions of high and .Comment: Accepted for publication in ApJ, using aaspp4.sty, 18 text pages with
9 figure
Mass Terms in Effective Theories of High Density Quark Matter
We study the structure of mass terms in the effective theory for
quasi-particles in QCD at high baryon density. To next-to-leading order in the
expansion we find two types of mass terms, chirality conserving
two-fermion operators and chirality violating four-fermion operators. In the
effective chiral theory for Goldstone modes in the color-flavor-locked (CFL)
phase the former terms correspond to effective chemical potentials, while the
latter lead to Lorentz invariant mass terms. We compute the masses of Goldstone
bosons in the CFL phase, confirming earlier results by Son and Stephanov as
well as Bedaque and Sch\"afer. We show that to leading order in the coupling
constant there is no anti-particle gap contribution to the mass of
Goldstone modes, and that our results are independent of the choice of gauge.Comment: 22 pages, 4 figure
Microbial ecology of Thiobacillus ferrooxidans
FINAL TECHNICAL REPORT
TO
U.S. DEPARTMENT OF THE INTERIOR
Geological Survey
Washington. D.C.The contents of this report were developed in part under a grant from
the Department of the Interior, U.S. Geological Survey. Grant number 14-08-0001-61313
Earth matter density uncertainty in atmospheric neutrino oscillations
That muon neutrinos oscillating into the mixture of tau neutrinos
and sterile neutrinos has been studied to explain the
atmospheric disappearance. In this scenario, the effect of Earth
matter is a key to determine the fraction of . Considering that the
Earth matter density has uncertainty and this uncertainty has significant
effects in some neutrino oscillation cases, such as the CP violation in very
long baseline neutrino oscillations and the day-night asymmetry for solar
neutrinos, we study the effects caused by this uncertainty in the above
atmospheric oscillation scenario. We find that this uncertainty
seems to have no significant effects and that the previous fitting results need
not to be modified fortunately.Comment: 7 pages, 1 figure, to appear in Phys. Rev.
Thermal quench effects on ferroelectric domain walls
Using piezoresponse force microscopy on epitaxial ferroelectric thin films,
we have measured the evolution of domain wall roughening as a result of
heat-quench cycles up to 735C, with the effective roughness exponent \zeta\
changing from 0.25 to 0.5. We discuss two possible mechanisms for the observed
\zeta\ increase: a quench from a thermal 1-dimensional configuration, and from
a locally-equilibrated pinned configuration with a crossover from a 2- to
1-dimensional regime. We find that the post-quench spatial structure of the
metastable states, qualitatively consistent with the existence of a growing
dynamical length scale whose ultra slow evolution is primarily controlled by
the defect configuration and heating process parameters, makes the second
scenario more plausible. This interpretation suggests that pinning is relevant
in a wide range of temperatures, and in particular, that purely thermal domain
wall configurations might not be observable in this glassy system. We also
demonstrate the crucial effects of oxygen vacancies in stabilizing domain
structures.Comment: 17 pages (preprint), 4 figure
Ultra narrow AuPd and Al wires
In this letter we discuss a novel and versatile template technique aimed to
the fabrication of sub-10 nm wide wires. Using this technique, we have
successfully measured AuPd wires, 12 nm wide and as long as 20 m. Even
materials that form a strong superficial oxide, and thus not suited to be used
in combination with other techniques, can be successfully employed. In
particular we have measured Al wires, with lateral width smaller or comparable
to 10 nm, and length exceeding 10 m.Comment: 4 pages, 4 figures. Pubblished in APL 86, 172501 (2005). Added
erratum and revised Fig.
Energy spectrum, density of states and optical transitions in strongly biased narrow-gap quantum wells
We study theoretically the effect of an electric field on the electron states
and far-infrared optical properties in narrow-gap lead salt quantum wells. The
electron states are described by a two-band Hamiltonian. An application of a
strong electric field across the well allows the control of the energy gap
between the two-dimensional (2D) states in a wide range. A sufficiently strong
electric field transforms the narrow-gap quantum well to a nearly gapless 2D
system, whose electron energy spectrum is described by linear dispersion
relations \epsilon_{\sigma} (k) ~\pm (k-k_{\sigma}), where k_{\sigma} are the
field-dependent 2D momenta corresponding to the minimum energy gaps for the
states with spin numbers \sigma. Due to the field-induced shift of the 2D
subband extrema away from k=0 the density of states has inverse-square-root
divergencies at the edges. This property may result in a considerable increase
of the magnitude of the optical absorption and in the efficiency of the
electrooptical effect.Comment: Text 18 pages in Latex/Revtex format, 7 Postscript figure
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