21,110 research outputs found
Long-Range Coulomb Effect on the Antiferromagnetism in Electron-doped Cuprates
Using mean-field theory, we illustrate the long-range Coulomb effect on the
antiferromagnetism in the electron-doped cuprates. Because of the Coulomb
exchange effect, the magnitude of the effective next nearest neighbor hopping
parameter increases appreciably with increasing the electron doping
concentration, raising the frustration to the antiferromagnetic ordering. The
Fermi surface evolution in the electron-doped cuprate NdCeCuO
and the doping dependence of the onset temperature of the antiferromagnetic
pseudogap can be reasonably explained by the present consideration.Comment: 4 pages, 4 figure
Effect of quantum fluctuations on structural phase transitions in SrTiO_3 and BaTiO_3
Using path-integral Monte Carol simulations and an ab initio effective
Hamiltonian, we study the effects of quantum fluctuations on structural phase
transitions in the cubic perovskite compounds SrTiO3 and BaTiO3. We find
quantum fluctuations affect ferroelectric (FE) transitions more strongly than
antiferrodistortive (AFD) ones, even though the effective mass of a single FE
local mode is larger. For SrTiO3 we find that the quantum fluctuations suppress
the FE transition completely, and reduce the AFD transition temperature from
130K to 110K. For BaTiO3, quantum fluctuations do not affect the order of the
transition, but do reduce the transition temperature by 35-50 K. The
implications of the calculations are discussed.Comment: Revtex (preprint style, 14 pages) + 2 postscript figures. A version
in two-column article style with embedded figures is available at
http://electron.rutgers.edu/~dhv/preprints/index.html#wz_qs
Twisted quantum affine algebras and solutions to the Yang-Baxter equation
We construct spectral parameter dependent R-matrices for the quantized
enveloping algebras of twisted affine Lie algebras. These give new solutions to
the spectral parameter dependent quantum Yang-Baxter equation.Comment: Latex 24 pages. Misprints in eqs.(4.26) and (A.11) are corrected,
cosmetic changes from "affine Kac-Moody algebras" to "affine Lie algebras"
are made throughout the paper following a suggestion by M.B. Halpern, and one
reference is adde
First-principles investigation of 180-degree domain walls in BaTiO_3
We present a first-principles study of 180-degree ferroelectric domain walls
in tetragonal barium titanate. The theory is based on an effective Hamiltonian
that has previously been determined from first-principles
ultrasoft-pseudopotential calculations. Statistical properties are investigated
using Monte Carlo simulations. We compute the domain-wall energy, free energy,
and thickness, analyze the behavior of the ferroelectric order parameter in the
interior of the domain wall, and study its spatial fluctuations. An abrupt
reversal of the polarization is found, unlike the gradual rotation typical of
the ferromagnetic case.Comment: Revtex (preprint style, 13 pages) + 3 postscript figures. A version
in two-column article style with embedded figures is available at
http://electron.rutgers.edu/~dhv/preprints/index.html#pad_wal
Solutions of the Yang-Baxter Equation with Extra Non-Additive Parameters II: }
The type-I quantum superalgebras are known to admit non-trivial one-parameter
families of inequivalent finite dimensional irreps, even for generic . We
apply the recently developed technique to construct new solutions to the
quantum Yang-Baxter equation associated with the one-parameter family of irreps
of , thus obtaining R-matrices which depend not only on a
spectral parameter but in addition on further continuous parameters. These
extra parameters enter the Yang-Baxter equation in a similar way to the
spectral parameter but in a non-additive form.Comment: 10 pages, LaTex file (some errors in the Casimirs corrected
On Type-I Quantum Affine Superalgebras
The type-I simple Lie-superalgebras are and . We study
the quantum deformations of their untwisted affine extensions
and . We identify additional
relations between the simple generators (``extra -Serre relations") which
need to be imposed to properly define \uqgh and . We
present a general technique for deriving the spectral parameter dependent
R-matrices from quantum affine superalgebras. We determine the R-matrices for
the type-I affine superalgebra in various representations,
thereby deriving new solutions of the spectral-dependent Yang-Baxter equation.
In particular, because this algebra possesses one-parameter families of
finite-dimensional irreps, we are able to construct R-matrices depending on two
additional spectral-like parameters, providing generalizations of the
free-fermion model.Comment: 23 page
Infinite Families of Gauge-Equivalent -Matrices and Gradations of Quantized Affine Algebras
Associated with the fundamental representation of a quantum algebra such as
or , there exist infinitely many gauge-equivalent
-matrices with different spectral-parameter dependences. It is shown how
these can be obtained by examining the infinitely many possible gradations of
the corresponding quantum affine algebras, such as and
, and explicit formulae are obtained for those two cases.
Spectral-dependent similarity (gauge) transformations relate the -matrices
in different gradations. Nevertheless, the choice of gradation can be
physically significant, as is illustrated in the case of quantum affine Toda
field theories.Comment: 14 pages, Latex, UQMATH-93-10 (final version for publication
First-principles study of stability and vibrational properties of tetragonal PbTiO_3
A first-principles study of the vibrational modes of PbTiO_3 in the
ferroelectric tetragonal phase has been performed at all the main symmetry
points of the Brillouin zone (BZ). The calculations use the local-density
approximation and ultrasoft pseudopotentials with a plane-wave basis, and
reproduce well the available experimental information on the modes at the Gamma
point, including the LO-TO splittings. The work was motivated in part by a
previously reported transition to an orthorhombic phase at low temperatures
[(J. Kobayashi, Y. Uesu, and Y. Sakemi, Phys. Rev. B {\bf 28}, 3866 (1983)]. We
show that a linear coupling of orthorhombic strain to one of the modes at Gamma
plays a role in the discussion of the possibility of this phase transition.
However, no mechanical instabilities (soft modes) are found, either at Gamma or
at any of the other high-symmetry points of the BZ.Comment: 8 pages, two-column style with 3 postscript figures embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#ag_pbt
Study of axial strain induced torsion of single wall carbon nanotubes by 2D continuum anharmonic anisotropic elastic model
Recent molecular dynamic simulations have found chiral single wall carbon
nanotubes (SWNTs) twist during stretching, which is similar to the motion of a
screw. Obviously this phenomenon, as a type of curvature-chirality effect, can
not be explained by usual isotropic elastic theory of SWNT. More interestingly,
with larger axial strains (before buckling), the axial strain induced torsion
(a-SIT) shows asymmetric behaviors for axial tensile and compressing strains,
which suggests anharmonic elasticity of SWNTs plays an important role in real
a-SIT responses. In order to study the a-SIT of chiral SWNTs with actual sizes,
and avoid possible deviations of computer simulation results due to the
finite-size effect, we propose a 2D analytical continuum model which can be
used to describe the the SWNTs of arbitrary chiralities, curvatures, and
lengths, with the concerning of anisotropic and anharmonic elasticity of SWNTs.
This elastic energy of present model comes from the continuum limit of lattice
energy based on Second Generation Reactive Empirical Bond Order potential
(REBO-II), a well-established empirical potential for solid carbons. Our model
has no adjustable parameters, except for those presented in REBO-II, and all
the coefficients in the model can be calculated analytically. Using our method,
we obtain a-SIT responses of chiral SWNTs with arbitrary radius, chiralities
and lengthes. Our results are in reasonable agreement with recent molecular
dynamic simulations. [Liang {\it et. al}, Phys. Rev. Lett, , 165501
(2006).] Our approach can also be used to calculate other curvature-chirality
dependent anharmonic mechanic responses of SWNTs.Comment: 14 pages, 2 figure
Multiparty Quantum Secret Sharing Based on Entanglement Swapping
A multiparty quantum secret sharing (QSS) protocol is proposed by using
swapping quantum entanglement of Bell states. The secret messages are imposed
on Bell states by local unitary operations. The secret messages are split into
several parts and each part is distributed to a party so that no action of a
subset of all the parties but their entire cooperation is able to read out the
secret messages. In addition, the dense coding is used in this protocol to
achieve a high efficiency. The security of the present multiparty QSS against
eavesdropping has been analyzed and confirmed even in a noisy quantum channel.Comment: 5 page
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