20,358 research outputs found
Odd Parity and Line Nodes in Heavy Fermion Superconductors
Group theory arguments have demonstrated that a general odd parity order
parameter cannot have line nodes in the presence of spin-orbit coupling. In
this paper, it is shown that these arguments do not hold on the
zone face of a hexagonal close packed lattice. In particular, three of the six
odd parity representations vanish identically on this face. This has potential
relevance to the heavy fermion superconductor .Comment: 5 pages, revte
Quasi-one and two-dimensional transitions of gases adsorbed on nanotube bundles
Grand canonical Monte Carlo simulations have been performed to determine the
adsorption behavior of Ar and Kr atoms on the exterior surface of a rope
(bundle) consisting of many carbon nanotubes. The computed adsorption isotherms
reveal phase transitions associated with the successive creation of quasi-one
dimensional lines of atoms near and parallel to the intersection of two
adjacent nanotubes.Comment: 12 pages, 6 figures, submitted to J. Chem. Phy
Technique for producing wind-tunnel heat-transfer models
Inexpensive thin skinned wind tunnel models with thermocouples on certain surface areas were fabricated. Thermocouples were designed for measuring aerodynamic heat transfer in wind tunnels
Odd Parity and Line Nodes in Non-Symmorphic Superconductors
Group theory arguments have been invoked to argue that odd parity order
parameters cannot have line nodes in the presence of spin-orbit coupling. In
this paper we show that these arguments do not hold for certain non-symmorphic
superconductors. Specifically, we demonstrate that when the underlying crystal
has a twofold screw axis, half of the odd parity representations vanish on the
Brillouin zone face perpendicular to this axis. Many unconventional
superconductors have non-symmorphic space groups, and we discuss implications
for several materials, including UPt3, UBe13, Li2Pt3B and Na4Ir3O8.Comment: 4 page
Magnetic resonance at 41 meV and charge dynamics in YBa_2Cu_3O_6.95
We report an Eliashberg analysis of the electron dynamics in YBa_2Cu_3O_6.95.
The magnetic resonance at 41 meV couples to charge carriers and defines the
characteristic shape in energy of the scattering rate \tau^{-1}(T,\omega) which
allows us to construct the charge-spin spectral density I^2\chi(\omega,T) at
temperature T. The T dependence of the weight under the resonance peak in
I^2\chi(\omega,T) agrees with experiment as does that of the London penetration
depth and of the microwave conductivity. Als, at T=0 condensation energy, the
fractional oscillator strength in the condensate, and the ratio of gap to
critical temperature agree well with the data.Comment: 7 Pages, 3 Figures, accepted for publication in Europhysics Letter
Reconstruction of the Fermi surface in the pseudogap state of cuprates
Reconstruction of the Fermi surface of high-temperature superconducting
cuprates in the pseudogap state is analyzed within nearly exactly solvable
model of the pseudogap state, induced by short-range order fluctuations of
antiferromagnetic (AFM, spin density wave (SDW), or similar charge density wave
(CDW)) order parameter, competing with superconductivity. We explicitly
demonstrate the evolution from "Fermi arcs" (on the "large" Fermi surface)
observed in ARPES experiments at relatively high temperatures (when both the
amplitude and phase of density waves fluctuate randomly) towards formation of
typical "small" electron and hole "pockets", which are apparently observed in
de Haas - van Alfen and Hall resistance oscillation experiments at low
temperatures (when only the phase of density waves fluctuate, and correlation
length of the short-range order is large enough). A qualitative criterion for
quantum oscillations in high magnetic fields to be observable in the pseudogap
state is formulated in terms of cyclotron frequency, correlation length of
fluctuations and Fermi velocity.Comment: 4 pages, 3 figure
The Temperature Evolution of the Spectral Peak in High Temperature Superconductors
Recent photoemission data in the high temperature cuprate superconductor
Bi2212 have been interpreted in terms of a sharp spectral peak with a
temperature independent lifetime, whose weight strongly decreases upon heating.
By a detailed analysis of the data, we are able to extract the temperature
dependence of the electron self-energy, and demonstrate that this intepretation
is misleading. Rather, the spectral peak loses its integrity above Tc due to a
large reduction in the electron lifetime.Comment: 5 pages, revtex, 4 encapsulated postscript figure
A Multi-Species Model for Hydrogen and Helium Absorbers in Lyman-Alpha Forest Clouds
We have performed a multi-species hydrodynamical simulation of the formation
and evolution of Lyman alpha clouds in a flat CDM dominated universe with an
external flux of ionizing radiation. We solve the fully coupled non-equilibrium
rate equations for the following species: H, H^+, H^-, H_2, H_2^+, He, He^+,
He^{++}, and e^-. The statistical properties of the distribution and evolution
of both hydrogen and helium absorption lines are extracted and compared to
observed data. We find excellent agreement for the following neutral hydrogen
data: the distribution of column densities is fit well by a power law with
exponent beta=1.55 with a possible deficiency of lines above column density
10^{15} cm^{-2}; the integrated distribution matches observed data over a broad
range of column densities 10^{13} to 10^{17} cm^{-2}; a Gaussian statistical
fit to the Doppler parameter distribution yields a median of 35.6 km s^{-1};
the evolution of the number of clouds with column densities larger than 10^{14}
cm^{-2} follows a power law with exponent gamma=2.22. Analogous calculations
are presented for HeII absorption lines and we find the ratio of Doppler
parameters b_{HeII}/b_{HI} = 0.87. Our data also suggests that Ly
clouds may belong to two morphologically different groups: small column density
clouds which tend to reside in sheets or filamental structures and are very
elongated and/or flattened, and the large column density clouds which are
typically found at the intersections of these caustic structures and are
quasi-spherical.Comment: 14 pages, 4 postscript figure
Temperature-dependent quantum pair potentials and their application to dense partially ionized hydrogen plasmas
Extending our previous work \cite{filinov-etal.jpa03ik} we present a detailed
discussion of accuracy and practical applications of finite-temperature
pseudopotentials for two-component Coulomb systems. Different pseudopotentials
are discussed: i) the diagonal Kelbg potential, ii) the off-diagonal Kelbg
potential iii) the {\em improved} diagonal Kelbg potential, iv) an effective
potential obtained with the Feynman-Kleinert variational principle v) the
``exact'' quantum pair potential derived from the two-particle density matrix.
For the {\em improved} diagonal Kelbg potential a simple temperature dependent
fit is derived which accurately reproduces the ``exact'' pair potential in the
whole temperature range. The derived pseudopotentials are then used in path
integral Monte Carlo (PIMC) and molecular dynamics (MD) simulations to obtain
thermodynamical properties of strongly coupled hydrogen. It is demonstrated
that classical MD simulations with spin-dependent interaction potentials for
the electrons allow for an accurate description of the internal energy of
hydrogen in the difficult regime of partial ionization down to the temperatures
of about K. Finally, we point out an interesting relation between the
quantum potentials and effective potentials used in density functional theory.Comment: 18 pages, 11 figure
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