7,996 research outputs found
First-Matsubara-frequency rule in a Fermi liquid. Part I: Fermionic self-energy
We analyze in detail the fermionic self-energy \Sigma(\omega, T) in a Fermi
liquid (FL) at finite temperature T and frequency \omega. We consider both
canonical FLs -- systems in spatial dimension D >2, where the leading term in
the fermionic self-energy is analytic [the retarded Im\Sigma^R(\omega,T) =
C(\omega^2 +\pi^2 T^2)], and non-canonical FLs in 1<D <2, where the leading
term in Im\Sigma^R(\omega,T) scales as T^D or \omega^D. We relate the \omega^2
+ \pi^2 T^2 form to a special property of the self-energy -"the
first-Matsubara-frequency rule", which stipulates that \Sigma^R(i\pi T,T) in a
canonical FL contains an O(T) but no T^2 term. We show that in any D >1 the
next term after O(T) in \Sigma^R(i\pi T,T) is of order T^D (T^3\ln T in D=3).
This T^D term comes from only forward- and backward scattering, and is
expressed in terms of fully renormalized amplitudes for these processes. The
overall prefactor of the T^D term vanishes in the "local approximation", when
the interaction can be approximated by its value for the initial and final
fermionic states right on the Fermi surface. The local approximation is
justified near a Pomeranchuk instability, even if the vertex corrections are
non-negligible. We show that the strength of the first-Matsubara-frequency rule
is amplified in the local approximation, where it states that not only the T^D
term vanishes but also that \Sigma^R(i\pi T,T) does not contain any terms
beyond O(T). This rule imposes two constraints on the scaling form of the
self-energy: upon replacing \omega by i\pi T, Im\Sigma^R(\omega,T) must vanish
and Re\Sigma^R (\omega, T) must reduce to O(T). These two constraints should be
taken into consideration in extracting scaling forms of \Sigma^R(\omega,T) from
experimental and numerical data.Comment: 22 pages, 3 figure
A scalable, high-speed measurement-based quantum computer using trapped ions
We describe a scalable, high-speed, and robust architecture for
measurement-based quantum-computing with trapped ions. Measurement-based
architectures offer a way to speed-up operation of a quantum computer
significantly by parallelizing the slow entangling operations and transferring
the speed requirement to fast measurement of qubits. We show that a 3D cluster
state suitable for fault-tolerant measurement-based quantum computing can be
implemented on a 2D array of ion traps. We propose the projective measurement
of ions via multi-photon photoionization for nanosecond operation and discuss
the viability of such a scheme for Ca ions.Comment: 4 pages, 3 figure
Fluctuations in the level density of a Fermi gas
We present a theory that accurately describes the counting of excited states
of a noninteracting fermionic gas. At high excitation energies the results
reproduce Bethe's theory. At low energies oscillatory corrections to the
many--body density of states, related to shell effects, are obtained. The
fluctuations depend non-trivially on energy and particle number. Universality
and connections with Poisson statistics and random matrix theory are
established for regular and chaotic single--particle motion.Comment: 4 pages, 1 figur
Probing the field-induced variation of the chemical potential in Bi(2)Sr(2)CaCu(2)O(y) via the magneto-thermopower measurements
Approximating the shape of the measured in
magneto-thermopower (TEP) by asymmetric linear triangle of the
form with positive and defined below and above , we observe that . In order to account for this asymmetry, we
explicitly introduce the field-dependent chemical potential of holes
into the Ginzburg-Landau theory and calculate both an average and fluctuation contributions to the total
magneto-TEP . As a result, we find a rather simple relationship
between the field-induced variation of the chemical potential in this material
and the above-mentioned magneto-TEP data around , viz. .Comment: REVTEX (epsf), 4 pages, 2 PS figures; to be published in JET
Hierarchical Model for the Evolution of Cloud Complexes
The structure of cloud complexes appears to be well described by a "tree
structure" representation when the image is partitioned into "clouds". In this
representation, the parent-child relationships are assigned according to
containment. Based on this picture, a hierarchical model for the evolution of
Cloud Complexes, including star formation, is constructed, that follows the
mass evolution of each sub-structure by computing its mass exchange
(evaporation or condensation) with its parent and children, which depends on
the radiation density at the interphase. For the set of parameters used as a
reference model, the system produces IMFs with a maximum at too high mass (~2
M_sun) and the characteristic times for evolution seem too long. We show that
these properties can be improved by adjusting model parameters. However, the
emphasis here is to illustrate some general properties of this nonlinear model
for the star formation process. Notwithstanding the simplifications involved,
the model reveals an essential feature that will likely remain if additional
physical processes are included. That is: the detailed behavior of the system
is very sensitive to variations on the initial and external conditions,
suggesting that a "universal" IMF is very unlikely. When an ensemble of IMFs
corresponding to a variety of initial or external conditions is examined, the
slope of the IMF at high masses shows variations comparable to the range
derived from observational data. (Abridged)Comment: Latex, 29 pages, 13 figures, accepted for publication in Ap
Weak Field Hall Resistance and Effective Carrier Density Through Metal-Insulator Transition in Si-MOS Structures
We studied the weak field Hall voltage in 2D electron layers in Si-MOS
structures with different mobilities, through the metal-insulator transition.
In the vicinity of the critical density on the metallic side of the transition,
we have found weak deviations (about 6-20 %) of the Hall voltage from its
classical value. The deviations do not correlate with the strong temperature
dependence of the diagonal resistivity rho_{xx}(T). The smallest deviation in
R_{xy} was found in the highest mobility sample exhibiting the largest
variation in the diagonal resistivity \rho_{xx} with temperature (by a factor
of 5).Comment: 4 pages, 4 figures, RevTe
Temperature and salinity tolerances of Stage 1 zoeae predict possible range expansion of an introduced portunid crab, Charybdis japonica, in New Zealand
The successful invasion of a non-native species depends on several factors, including initial colonization and establishment of a self-sustaining population. Populations of the non-native paddle crab Charybdis japonica were first recognized in the Waitemata Harbour, Auckland, New Zealand in 2000, most likely arriving in ballast waters of an Asian merchant vessel. A survey completed in 2003 found C. japonica throughout the Waitemata Harbour, and further sampling in 2009 has revealed several well established populations in estuaries up to 70 km from the putative invasion point. As the potential for further establishment of C. japonica beyond this area may depend on the temperature and salinity tolerances of their free swimming larvae, we quantified the survival of newly-hatched Stage 1 C. japonica zoeae subjected to temperatures ranging from 11 to 43°C or salinities from 5 to 45‰ in the laboratory. Upon hatching, replicate C. japonica zoeae were directly transferred from 21°C and 34.6‰ seawater to either an experimental temperature or salinity level. Behaviour and death rates of the larvae were monitored over a 24 h period in the absence of food. Comparisons of zoeal survival rates to historical sea surface temperatures and salinities show that C. japonica Stage 1 zoeae tolerate a broad range of temperatures and salinities and could survive natural conditions throughout New Zealand. This gives C. japonica the potential to invade many other New Zealand estuaries and harbours
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