51,665 research outputs found
Spin-Driven Nematic Instability of the Multi-Orbital Hubbard Model: Application to Iron-Based Superconductors
Nematic order resulting from the partial melting of density-waves has been
proposed as the mechanism to explain nematicity in iron-based superconductors.
An outstanding question, however, is whether the microscopic electronic model
for these systems -- the multi-orbital Hubbard model -- displays such an
ordered state as its leading instability. In contrast to usual electronic
instabilities, such as magnetic and charge order, this fluctuation-driven
phenomenon cannot be captured by the standard RPA method. Here, by including
fluctuations beyond RPA in the multi-orbital Hubbard model, we derive its
nematic susceptibility and contrast it with its ferro-orbital order
susceptibility, showing that its leading instability is the spin-driven nematic
phase. Our results also demonstrate the primary role played by the
orbital in driving the nematic transition, and reveal that high-energy magnetic
fluctuations are essential to stabilize nematic order in the absence of
magnetic order.Comment: 8 pages, 6 figure
Gauge/String-Gravity Duality and Froissart Bound
The gauge/string-gravity duality correspondence opened renewed hope and
possibility to address some of the fundamental and non-perturbative QCD
problems in particle physics, such as hadron spectrum and Regge behavior of the
scattering amplitude at high energies. One of the most fundamental and
long-standing problem is the high energy behavior of total cross-sections.
According to a series of exhaustive tests by the COMPETE group, (1). total
cross-sections have a universal Heisenberg behavior in energy corresponding to
the maximal energy behavior allowed by the Froissart bound, i.e., with and for all reactions,
and (2). the factorization relation among is well satisfied by experiments. I discuss the
recent interesting application of the gauge/string-gravity duality of
correspondence with a deformed background metric so as to break the conformal
symmetry that can lead to the Heisenberg behavior of rising total
cross-sections, and present some preliminary results on the high energy QCD
from Planckian scattering in and black-hole production.Comment: 10 pages, Presented to the Coral Gables Conference 2003, Launching of
BelleE\'poque in High Energy Physics and Cosmology, 17 - 21 December 2003,
Fort Lauderdale, Florid
Correlation Assisted Phonon Softenings and the Mott-Peierls Transition in VO
To explore the driving mechanisms of the metal-insulator transition (MIT) and
the structural transition in VO2, we have investigated phonon dispersions of
rutile VO2 (R-VO2) in the DFT and the DFT+U (U : Coulomb correlation) band
calculations. We have found that the phonon softening instabilities occur in
both cases, but the softened phonon mode only in the DFT+U describes properly
both the MIT and the structural transition from R-VO2 to monoclinic VO2
(M1-VO2). This feature demonstrates that the Coulomb correlation effect plays
an essential role of assisting the Peierls transition in R-VO2. We have also
found from the phonon dispersion of M1-VO2 that M1 structure becomes unstable
under high pressure. We have predicted a new phase of VO2 at high pressure that
has a monoclinic CaCl2-type structure with metallic nature
An alternative formulation of classical electromagnetic duality
By introducing a doublet of electromagnetic four dimensional vector
potentials, we set up a manifestly Lorentz covariant and SO(2) duality
invariant classical field theory of electric and magnetic charges. In our
formulation one does not need to introduce the concept of Dirac string.Comment: 14 pages, no figures, Latex, minor corrections, references and
acknowledgements adde
Reaction-diffusion with a time-dependent reaction rate: the single-species diffusion-annihilation process
We study the single-species diffusion-annihilation process with a
time-dependent reaction rate, lambda(t)=lambda_0 t^-omega. Scaling arguments
show that there is a critical value of the decay exponent omega_c(d) separating
a reaction-limited regime for omega > omega_c from a diffusion-limited regime
for omega < omega_c. The particle density displays a mean-field,
omega-dependent, decay when the process is reaction limited whereas it behaves
as for a constant reaction rate when the process is diffusion limited. These
results are confirmed by Monte Carlo simulations. They allow us to discuss the
scaling behaviour of coupled diffusion-annihilation processes in terms of
effective time-dependent reaction rates.Comment: 11 pages, 9 figures, minor correction
Defect Motion and Lattice Pinning Barrier in Josephson-Junction Ladders
We study motion of domain wall defects in a fully frustrated
Josephson-unction ladder system, driven by small applied currents. For small
system sizes, the energy barrier E_B to the defect motion is computed
analytically via symmetry and topological considerations. More generally, we
perform numerical simulations directly on the equations of motion, based on the
resistively-shunted junction model, to study the dynamics of defects, varying
the system size. Coherent motion of domain walls is observed for large system
sizes. In the thermodynamical limit, we find E_B=0.1827 in units of the
Josephson coupling energy.Comment: 7 pages, and to apear in Phys. Rev.
Prefeasibility study of a space environment monitoring system /Semos/
Prefeasibility study of Space Environment Monitoring System within framework of Apollo Applications Progra
Characterization of a novel reassortant H5N6 highly pathogenic avian influenza virus clade 2.3.4.4 in Korea, 2017
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