42,941 research outputs found
Relationship between single-particle excitation and spin excitation at the Mott Transition
An intuitive interpretation of the relationship between the dispersion
relation of the single-particle excitation in a metal and that of the spin
excitation in a Mott insulator is presented, based on the results for the one-
and two-dimensional Hubbard models obtained by using the Bethe ansatz,
dynamical density-matrix renormalization group method, and cluster perturbation
theory. The dispersion relation of the spin excitation in the Mott insulator is
naturally constructed from that of the single-particle excitation in the
zero-doping limit in both one- and two-dimensional Hubbard models, which allows
us to interpret the doping-induced states as the states that lose charge
character toward the Mott transition. The characteristic feature of the Mott
transition is contrasted with the feature of a Fermi liquid and that of the
transition between a band insulator and a metal.Comment: 6 pages, 2 figures, to appear in JPS Conf. Pro
Trans-Magnetosonic Accretion in a Black Hole Magnetosphere
We present the critical conditions for hot trans-fast magnetohydrodynamical
(MHD) flows in a stationary and axisymmetric black-hole magnetosphere. To
accrete onto the black hole, the MHD flow injected from a plasma source with
low velocity must pass through the fast magnetosonic point after passing
through the ``inner'' or ``outer'' Alfven point. We find that a trans-fast MHD
accretion solution related to the inner Alfven point is invalid when the
hydrodynamical effects on the MHD flow dominate at the magnetosonic point,
while the other accretion solution related to the outer Alfven point is invalid
when the total angular momentum of the MHD flow is seriously large. When both
regimes of the accretion solutions are valid in the black hole magnetosphere,
we can expect the transition between the two regimes. The variety of these
solutions would be important in many highly energetic astrophysical situations.Comment: 27 pages, 12 figures, accepted to Ap
Mesoscopic conductance fluctuations in a coupled quantum dot system
We study the transport properties of an Aharonov-Bohm ring containing two
quantum dots. One of the dots has well-separated resonant levels, while the
other is chaotic and is treated by random matrix theory. We find that the
conductance through the ring is significantly affected by mesoscopic
fluctuations. The Breit-Wigner resonant peak is changed to an antiresonance by
increasing the ratio of the level broadening to the mean level spacing of the
random dot. The asymmetric Fano form turns into a symmetric one and the
resonant peak can be controlled by magnetic flux. The conductance distribution
function clearly shows the influence of strong fluctuations.Comment: 4 pages, 4 figures; revised for publicatio
Biquadratic antisymmetric exchange and the magnetic phase diagram of magnetoelectric CuFeO
Biquadratic {\it antisymmetric} exchange terms of the form , where is the
unit vector connecting sites and and , due partially to
magnetoelectric coupling effects, are shown to be responsible for the spin-flop
helical phase in CuFeO at low magnetic field and temperature. Usual
biquadratic {\it symmetric} exchange, likely due to magnetoelastic coupling, is
found to support the stability of axial magnetic states at higher fields in
this nearly-Heisenberg like stacked triangular antiferromagnet. A model
Hamiltonian which also includes substantial interplane and higher-neighbor
intraplane exchange interactions, reproduces the unique series of observed
commensurate and incommensurate periodicity phases with increasing applied
magnetic field in this highly frustrated system. The magnetic field-temperature
phase diagram is discussed in terms of a Landau-type free energy.Comment: 7 pages, 9 figure
Pre-K-Edge Structure on Anomalous X-Ray Scattering in LaMnO3
We study the pre-K-edge structure of the resonant X-ray scattering for
forbidden reflections (anomalous scattering) in LaMnO3, using the band
calculation based on the local density approximation. We find a two-peak
structure with an intensity approximately 1/100 of that of the main peak. This
originates from a mixing of 4p states of Mn to 3d states of neighboring Mn
sites. The effect is enhanced by an interference with the tail of the main
peak. The effect of the quadrupole transition is found to be one order of
magnitude smaller than that of the dipole transition, modifying slightly the
azimuthal-angle dependence.Comment: 4 pages, 5 figures, submitted to J. Phys. Soc. Jp
Spectral Properties near the Mott Transition in the One-Dimensional Hubbard Model
Single-particle spectral properties near the Mott transition in the
one-dimensional Hubbard model are investigated by using the dynamical
density-matrix renormalization group method and the Bethe ansatz. The
pseudogap, hole-pocket behavior, spectral-weight transfer, and upper Hubbard
band are explained in terms of spinons, holons, antiholons, and doublons. The
Mott transition is characterized by the emergence of a gapless mode whose
dispersion relation extends up to the order of hopping t (spin exchange J) in
the weak (strong) interaction regime caused by infinitesimal doping.Comment: 4 pages, 2 figure
Quantum Spin Chains and Riemann Zeta Function with Odd Arguments
Riemann zeta function is an important object of number theory. It was also
used for description of disordered systems in statistical mechanics. We show
that Riemann zeta function is also useful for the description of integrable
model. We study XXX Heisenberg spin 1/2 anti-ferromagnet. We evaluate a
probability of formation of a ferromagnetic string in the anti-ferromagnetic
ground state in thermodynamics limit. We prove that for short strings the
probability can be expressed in terms of Riemann zeta function with odd
arguments.Comment: LaTeX, 7 page
Magnetic susceptibility and low-temperature specific-heat of integrable 1-D Hubbard model under open-boundary conditions
The magnetic susceptibility and the low-temperature specific heat of the
1-dimensional Hubbard model under the integrable open-boundary conditions are
discussed through the Bethe ansatz with the string hypothesis. The
contributions of the boundary fields to both the susceptibility and the
specific heat are obtained, and their exact expressions are analytically
derived.Comment: 14 pages, Latex, No figures, to appear in J. Phys. A: Gen. & Mat
Order-disorder transition in nanoscopic semiconductor quantum rings
Using the path integral Monte Carlo technique we show that semiconductor
quantum rings with up to six electrons exhibit a temperature, ring diameter,
and particle number dependent transition between spin ordered and disordered
Wigner crystals. Due to the small number of particles the transition extends
over a broad temperature range and is clearly identifiable from the electron
pair correlation functions.Comment: 4 pages, 5 figures, For recent information on physics of small
systems see http://www.smallsystems.d
Paired state in an integrable spin-1 boson model
An exactly solvable model describing the low density limit of the spin-1
bosons in a one-dimensional optical lattice is proposed. The exact Bethe ansatz
solution shows that the low energy physics of this system is described by a
quantum liquid of spin singlet bound pairs. Motivated by the exact results, a
mean-field approach to the corresponding three-dimensional system is carried
out. Condensation of singlet pairs and coexistence with ordinary Bose-Einstein
condensation are predicted.Comment: 6 pages, 1 figure, Revised versio
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