585 research outputs found
Universal scaling behavior of the single electron box in the strong tunneling limit
We perform a numerical analysis of recently proposed scaling functions for
the single electron box. Specifically, we study the ``magnetic'' susceptibility
as a function of tunneling conductance and gate charge, and the effective
charging energy at zero gate charge as a function of tunneling conductance in
the strong tunneling limit. Our Monte Carlo results confirm the accuracy of the
theoretical predictions.Comment: Published versio
Asymptotic tunneling conductance in Luttinger liquids
Conductance through weak constrictions in Luttinger liquids is shown to
vanish with frequency as , where
is a dimensionless parameter characterizing the Luttinger liquid phase, and
and are nonuniversal constants. The first term arises from the ^^
Coulomb blockade' effect and dominates for , whereas the second
results from eliminating high-energy modes and dominates for .Comment: Latex file + one appended postcript figur
Brzozowski Algorithm Is Generically Super-Polynomial Deterministic Automata
International audienceWe study the number of states of the minimal automaton of the mirror of a rational language recognized by a random deterministic automaton with n states. We prove that, for any d > 0, the probability that this number of states is greater than nd tends to 1 as n tends to infinity. As a consequence, the generic and average complexities of Brzozowski minimization algorithm are super-polynomial for the uniform distribution on deterministic automata
quantum Heisenberg antiferromagnet on the triangular lattice: a group symmetry analysis of order by disorder
On the triangular lattice, for between and , the classical
Heisenberg model with first and second neighbor interactions presents
four-sublattice ordered ground-states. Spin-wave calculations of Chubukov and
Jolicoeur\cite{cj92} and Korshunov\cite{k93} suggest that quantum fluctuations
select amongst these states a colinear two-sublattice order. From theoretical
requirements, we develop the full symmetry analysis of the low lying levels of
the spin-1/2 Hamiltonian in the hypotheses of either a four or a two-sublattice
order. We show on the exact spectra of periodic samples ( and )
how quantum fluctuations select the colinear order from the four-sublattice
order.Comment: 15 pages, 4 figures (available upon request), Revte
Anisotropic quasiparticle lifetimes in Fe-based superconductors
We study the dynamical quasiparticle scattering by spin and charge
fluctuations in Fe-based pnictides within a five-orbital model with on-site
interactions. The leading contribution to the scattering rate is calculated
from the second-order diagrams with the polarization operator calculated in the
random-phase approximation. We find one-particle scattering rates which are
highly anisotropic on each Fermi surface sheet due to the momentum dependence
of the spin susceptibility and the multi-orbital composition of each Fermi
pocket. This fact, combined with the anisotropy of the effective mass, produces
disparity between electrons and holes in conductivity, the Hall coefficient,
and the Raman initial slope, in qualitative agreement with experimental data.Comment: 10 pages, 9 figure
Boson pairing and unusual criticality in a generalized XY model
We discuss the unusual critical behavior of a generalized XY model containing
both 2\pi-periodic and \pi-periodic couplings between sites. The presence of
vortices and half-vortices allows for single-particle condensate and
pair-condensate phases. Using a field theoretic formulation and worm algorithm
Monte Carlo simulations, we show that in two dimensions it is possible for the
system to pass directly from the disordered (high temperature) phase to the
single particle (quasi)-condensate via an Ising transition, a situation
reminiscent of the `deconfined criticality' scenario.Comment: Published versio
Fluctuation induced vortex pattern and its disordering in the fully frustrated XY model on a dice lattice
A highly degenerate family of states [proposed in PRB 63, 134503 (2001)] is
proven to really minimize the Hamiltonian of the fully frustrated XY model on a
dice lattice. The harmonic fluctuations are shown to be no consequence for the
removal of the accidental degeneracy of these states, so a particular vortex
pattern can be stabilized only by the anharmonic fluctuations. The structure of
this pattern is found and the temperature of its disordering due to the
proliferation of domain walls is estimated. The extreme smallness of the
fluctuations induced free energy of domain walls leads to the anomalous
prominence of the finite-size effects, which prevent the observation of
vortex-pattern ordering in numerical simulations. In such a situation the loss
of phase coherence may be related to the dissociation of fractional vortices
with topological charges 1/8. In a physical situation the magnetic interaction
of currents in a Josephson junction array will be a more important source for
the stabilization of a particular vortex pattern than the anharmonic
fluctuations.Comment: 20 pages, 7 figure
Electron-phonon interaction in the lamellar cobaltate NaCoO
We study theoretically and experimentally the dependence of the
electron-phonon interaction in NaCoO on the sodium concentration .
For the two oxygen phonon modes found in Raman experiments, and
, we calculate the matrix elements of the electron-phonon interaction.
Analyzing the feedback effect of the conduction electrons on the phonon
frequency we compare the calculated and experimentally observed doping
dependence of the mode. Furthermore, due to the momentum dependence of
the electron-phonon coupling for the symmetry we find no
renormalization of the corresponding phonon frequency which agrees with
experiment. Our results shed light on the possible importance of the
electron-phonon interaction in this system.Comment: 5 pages, 2 figures (submitted to PRB
Phase transitions in the antiferromagnetic XY model with a kagome lattice
The ground state of the antiferromagnetic XY model with a kagome lattice is
characterized by a well developed accidental degeneracy. As a consequence the
phase transition in this system consists in unbinding of pairs of fractional
vortices. Addition of the next-to-nearest neighbors (NNN) interaction leads to
stabilization of the long-range order in chirality (staggered chirality). We
show that the phase transition, related with destruction of this long-range
order, can happen as a separate phase transition below the temperature of the
fractional vortex pairs unbinding only if the NNN coupling is extremely weak,
and find how the temperature of this transition depends on coupling constants.
We also demonstarte that the antiferromagnetic ordering of chiralities and,
accordingly, the presence of the second phase transition are induced by the
free energy of spin wave fluctuations even in absence of the NNN coupling.Comment: 10 pages (Revtex) + 8 figures (in 2 postscript files
МОДЕЛИРОВАНИЕ РАДИАЦИОННОЙ СТОЙКОСТИ ЭЛЕМЕНТОВ ЛОГИЧЕСКИХ КМОП ИНТЕГРАЛЬНЫХ МИКРОСХЕМ
The software to simulate radiation resistance of MOSFET transistors, the basic elements of CMOS integrated circuits, is presented. The software performs visualization and analysis of volt-ampere characteristics of p - and n -channel transistors, extraction of «radiation sensitive» SPICE parameters and modeling of their variations with an ionizing radiation. The degradation of MOSFET transistors of the 1554LN1 microcircuit is investigated for gamma Co60 irradiation.Приведено описание программного комплекса для моделирования радиационной стойкости n - и p -канальных металл-окисел-полупроводник (МОП) транзисторов - элементов комплементарных МОП интегральных микросхем. Программное обеспечение предназначено для визуализации и анализа результатов измерений вольтамперных характеристик транзисторов, экстракции SPICE-параметров и последующего моделирования их эволюции в зависимости от дозы ионизирующего излучения. Исследовано радиационное поведение МОП транзисторов - элементов микросхем 1554ЛН1 - в поле ионизирующего излучения Со60
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