2,543 research outputs found
Dynamics of an Acoustic Polaron in One-Dimensional Electron-Lattice System
The dynamical behavior of an acoustic polaron in typical non-degenerate
conjugated polymer, polydiacetylene, is numerically studied by using
Su-Schrieffer-Heeger's model for the one dimensional electron-lattice system.
It is confirmed that the velocity of a polaron accelerated by a constant
electric field shows a saturation to a velocity close to the sound velocity of
the system, and that the width of a moving polaron decreases as a monotonic
function of the velocity tending to zero at the saturation velocity. The
effective mass of a polaron is estimated to be about one hundred times as heavy
as the bare electron mass. Furthermore the linear mode analysis in the presence
of a polaron is carried out, leading to the conclusion that there is only one
localized mode, i.e. the translational mode. This is confirmed also from the
phase shift of extended modes. There is no localized mode corresponding to the
amplitude mode in the case of the soliton in polyacetylene. Nevertheless the
width of a moving polaron shows small oscillations in time. This is found to be
related to the lowest odd symmetry extended mode and to be due to the finite
size effect.Comment: 12 pages, latex, 9 figures (postscript figures abailble on request to
[email protected]) to be published in J. Phys. Soc. Jpn. vol.65
(1996) No.
The anomalous behavior of coefficient of normal restitution in the oblique impact
The coefficient of normal restitution in an oblique impact is theoretically
studied. Using a two-dimensional lattice models for an elastic disk and an
elastic wall, we demonstrate that the coefficient of normal restitution can
exceed one and has a peak against the incident angle in our simulation.
Finally, we explain these phenomena based upon the phenomenological theory of
elasticity.Comment: 4 pages, 4 figures, to be appeared in PR
Saari's homographic conjecture for planar equal-mass three-body problem in Newton gravity
Saari's homographic conjecture in N-body problem under the Newton gravity is
the following; configurational measure \mu=\sqrt{I}U, which is the product of
square root of the moment of inertia I=(\sum m_k)^{-1}\sum m_i m_j r_{ij}^2 and
the potential function U=\sum m_i m_j/r_{ij}, is constant if and only if the
motion is homographic. Where m_k represents mass of body k and r_{ij}
represents distance between bodies i and j. We prove this conjecture for planar
equal-mass three-body problem.
In this work, we use three sets of shape variables. In the first step, we use
\zeta=3q_3/(2(q_2-q_1)) where q_k \in \mathbb{C} represents position of body k.
Using r_1=r_{23}/r_{12} and r_2=r_{31}/r_{12} in intermediate step, we finally
use \mu itself and \rho=I^{3/2}/(r_{12}r_{23}r_{31}). The shape variables \mu
and \rho make our proof simple
Photogeneration Dynamics of a Soliton Pair in Polyacetylene
Dynamical process of the formation of a soliton pair from a photogenerated
electron-hole pair in polyacetylene is studied numerically by adopting the SSH
Hamiltonian. A weak local disorder is introduced in order to trigger the
formation. Starting from an initial configuration with an electron at the
bottom of the conduction band and a hole at the top of the valence band,
separated by the Peierls gap, the time dependent Schrndinger
equation for the electron wave functions and the equation of motion for the
lattice displacements are solved numerically. After several uniform
oscillations of the lattice system at the early stage, a large distortion
corresponding to a pair of a soliton and an anti-soliton develops from a point
which is determined by the location and type of the disorder. In some cases,
two solitons run in opposite directions, leaving breather like oscillations
behind, and in other cases they form a bound state emitting acoustic lattice
vibrational modes.Comment: 16 pages 7 figure
Magnetic translation groups in an n-dimensional torus
A charged particle in a uniform magnetic field in a two-dimensional torus has
a discrete noncommutative translation symmetry instead of a continuous
commutative translation symmetry. We study topology and symmetry of a particle
in a magnetic field in a torus of arbitrary dimensions. The magnetic
translation group (MTG) is defined as a group of translations that leave the
gauge field invariant. We show that the MTG on an n-dimensional torus is
isomorphic to a central extension of a cyclic group Z_{nu_1} x ... x
Z_{nu_{2l}} x T^m by U(1) with 2l+m=n. We construct and classify irreducible
unitary representations of the MTG on a three-torus and apply the
representation theory to three examples. We shortly describe a representation
theory for a general n-torus. The MTG on an n-torus can be regarded as a
generalization of the so-called noncommutative torus.Comment: 29 pages, LaTeX2e, title changed, re-organized, to be published in
Journal of Mathematical Physic
Electronic theory for the normal state spin dynamics in SrRuO: anisotropy due to spin-orbit coupling
Using a three-band Hubbard Hamiltonian we calculate within the
random-phase-approximation the spin susceptibility, , and
NMR spin-lattice relaxation rate, 1/T, in the normal state of the triplet
superconductor SrRuO and obtain quantitative agreement with
experimental data. Most importantly, we find that due to spin-orbit coupling
the out-of-plane component of the spin susceptibility becomes at
low temperatures two times larger than the in-plane one. As a consequence
strong incommensurate antiferromagnetic fluctuations of the
quasi-one-dimensional - and -bands point into the -direction. Our
results provide further evidence for the importance of spin fluctuations for
triplet superconductivity in SrRuO.Comment: revised versio
A crib-shaped triplet pairing gap function for an orthogonal pair of quasi-one dimensional Fermi surfaces in SrRuO
The competition between spin-triplet and singlet pairings is studied
theoretically for the tight-binding - bands in SrRuO,
which arise from two sets of quasi-one dimensional Fermi surfaces. Using
multiband FLEX approximation, where we incorporate an anisotropy in the spin
fluctuations as suggested from experiments, we show that (i) the triplet can
dominate over the singlet (which turns out to be extended s), and (ii) the
triplet gap function optimized in the Eliashberg equation has an unusual, very
non-sinusoidal form, whose time-reversal-broken combination exhibits a
crib-shaped amplitude with dips.Comment: 5 pages, RevTeX, to appear in Phys.Rev.B (Rapid Communications
Anisotropy in the Antiferromagnetic Spin Fluctuations of Sr2RuO4
It has been proposed that Sr_2RuO_4 exhibits spin triplet superconductivity
mediated by ferromagnetic fluctuations. So far neutron scattering experiments
have failed to detect any clear evidence of ferromagnetic spin fluctuations
but, instead, this type of experiments has been successful in confirming the
existence of incommensurate spin fluctuations near q=(1/3 1/3 0). For this
reason there have been many efforts to associate the contributions of such
incommensurate fluctuations to the mechanism of its superconductivity. Our
unpolarized inelastic neutron scattering measurements revealed that these
incommensurate spin fluctuations possess c-axis anisotropy with an anisotropic
factor \chi''_{c}/\chi''_{a,b} of \sim 2.8. This result is consistent with some
theoretical ideas that the incommensurate spin fluctuations with a c-axis
anisotropy can be a origin of p-wave superconductivity of this material.Comment: 5 pages, 3 figures; accepted for publication in PR
Spin-triplet superconductivity due to antiferromagnetic spin-fluctuation in Sr_2RuO_4
A mechanism leading to the spin-triplet superconductivity is proposed based
on the antiferromagnetic spin fluctuation. The effects of anisotropy in spin
fluctuation on the Cooper pairing and on the direction of d vector are examined
in the one-band Hubbard model with RPA approximation. The gap equations for the
anisotropic case are derived and applied to Sr_2RuO_4. It is found that a
nesting property of the Fermi surface together with the anisotropy leads to the
triplet superconductivity with the d=z(sin{k_x}\pm isin{k_y}), which is
consistent with experiments.Comment: 4 pages, 3 eps figures, revte
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