7,811 research outputs found
Ab initio study of shock compressed oxygen
Quantum molecular dynamic simulations are introduced to study the shock
compressed oxygen. The principal Hugoniot points derived from the equation of
state agree well with the available experimental data. With the increase of
pressure, molecular dissociation is observed. Electron spin polarization
determines the electronic structure of the system under low pressure, while it
is suppressed around 30 50 GPa. Particularly, nonmetal-metal transition
is taken into account, which also occurs at about 30 50 GPa. In
addition, the optical properties of shock compressed oxygen are also discussed.Comment: 5 pages, 5 figure
Pseudo-magnetoexcitons in strained graphene bilayers without external magnetic fields
The structural and electronic properties of graphene leads its charge
carriers to behave like relativistic particles, which is described by a
Dirac-like Hamiltonian. Since graphene is a monolayer of carbon atoms, the
strain due to elastic deformations will give rise to so-called `pseudomagnetic
fields (PMF)' in graphene sheet, and that has been realized experimentally in
strained graphene sample. Here we propose a realistic strained graphene bilayer
(SGB) device to detect the pseudo-magnetoexcitons (PME) in the absence of
external magnetic field. The carriers in each graphene layer suffer different
strong PMFs due to strain engineering, which give rise to Landau quantization.
The pseudo-Landau levels (PLLs) of electron-hole pair under inhomogeneous PMFs
in SGB are analytically obtained in the absence of Coulomb interactions. Based
on the general analytical optical absorption selection rule for PME, we show
that the optical absorption spectrums can interpret the corresponding formation
of Dirac-type PME. We also predict that in the presence of inhomogeneous PMFs,
the superfluidity-normal phase transition temperature of PME is greater than
that under homogeneous PMFs.}Comment: 16 pages, 6 figure
Estimating the central charge from the R\'enyi entanglement entropy
We calculate the von Neumann and R\'enyi bipartite entanglement entropy of
the model with a chemical potential on a 1+1 dimensional Euclidean
lattice with open and periodic boundary conditions. We show that the
Calabrese-Cardy conformal field theory predictions for the leading logarithmic
scaling with the spatial size of these entropies are consistent with a central
charge . This scaling survives the time continuum limit and truncations of
the microscopic degrees of freedom, modifications which allow us to connect the
Lagrangian formulation to quantum Hamiltonians. At half-filling, the forms of
the subleading corrections imposed by conformal field theory allow the
determination of the central charge with an accuracy better than two percent
for moderately sized lattices. We briefly discuss the possibility of estimating
the central charge using quantum simulators.Comment: 10 pages, 8 figures, 3 table
Orbital magnetization and its effect in antiferromagnets on the distorted fcc lattice
We study the intrinsic orbital magnetization (OM) in antiferromagnets on the
distorted face-centered-cubic lattice. The combined lattice distortion and spin
frustration induce nontrivial -space Chern invariant, which turns to result
in profound effects on the OM properties. We derive a specific relation between
the OM and the Hall conductivity, according to which it is found that the
intrinsic OM vanishes when the electron chemical potential lies in the Mott
gap. The distinct behavior of the intrinsic OM in the metallic and insulating
regions is shown. The Berry phase effects on the thermoelectric transport is
also discussed.Comment: 18 pages, 6 figure
Quark mass density- and temperature- dependent model for strange quark matter
It is found that the radius of a stable strangelet decreases as the
temperature increases in a quark mass density-dependent model. To overcome this
difficulty, we extend this model to a quark mass density- and temperature-
dependent model in which the vacuum energy density at zero baryon density limit
B depends on temperature. An ansatz is introduced and the regions for the best
choice of the parameters are studied.Comment: 5 pages, 4 figure
Regularization of Electroweak Monopole by Charge Screening and BPS Energy Bound
We show that the electroweak monopole can be regularized with a non-vacuum
electromagnetic permittivity. This allows us to set a new BPS bound for the
monopole mass, which implies that the mass may not be smaller than 2.98 TeV,
more probably 3.75 TeV. We demonstrate that the same method can also regularize
the Dirac monopole, which enhances the possibility to construct the Dirac
monopole of mass of a few hundred meV in condensed matters. We discuss the
physical implications of our result
Quantum molecular dynamics simulations for the nonmetal-metal transition in shocked methane
We have performed quantum molecular-dynamics simulations for methane under
shock compressions up to 80 GPa. We obtain good agreement with available
experimental data for the principal Hugoniot, derived from the equation of
state. A systematic study of the optical conductivity spectra, one-particle
density of states, and the distributions of the electronic charge over
supercell at Hugoniot points shows that the transition of shocked methane to a
metallic state takes place close to the density at which methane dissociates
significantly into molecular hydrogen and some long alkane chains. Through
analyzing the pair correlation function, we predict the chemical picture of the
shocked methane. In contrast to usual assumptions used for high pressure
modeling of methane, we find that no diamond-like configurations occurs for the
whole density-temperature range studied.Comment: Some revisions have been given in response to referees' sugestion
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