9,364 research outputs found
Canonical treatment of two dimensional gravity as an anomalous gauge theory
The extended phase space method of Batalin, Fradkin and Vilkovisky is applied
to formulate two dimensional gravity in a general class of gauges. A BRST
formulation of the light-cone gauge is presented to reveal the relationship
between the BRST symmetry and the origin of current algebra. From the
same principle we derive the conformal gauge action suggested by David, Distler
and Kawai.Comment: 11 pages, KANAZAWA-92-1
Ferromagnetism and orbital order in the two-orbital Hubbard model
We investigate spin and orbital states of the two-orbital Hubbard model on a
square lattice by using a variational Monte Carlo method at quarter-filling,
i.e., the electron number per site is one. As a variational wave function, we
consider a Gutzwiller projected wave function of a mean-field type wave
function for a staggered spin and/or orbital ordered state. Then, we evaluate
expectation value of energy for the variational wave functions by using the
Monte Carlo method and determine the ground state. In the strong Coulomb
interaction region, the ground state is the perfect ferromagnetic state with
antiferro-orbital (AF-orbital) order. By decreasing the interaction, we find
that the disordered state becomes the ground state. Although we have also
considered the paramagnetic state with AF-orbital order, i.e., purely orbital
ordered state, and partial ferromagnetic states with and without AF-orbital
order, they do not become the ground state.Comment: 4 pages, 1 figure, accepted for publication in Journal of Physics:
Conference Serie
Multipole correlations in low-dimensional f-electron systems
By using a density matrix renormalization group method, we investigate the
ground-state properties of a one-dimensional three-orbital Hubbard model on the
basis of a j-j coupling scheme. For , where is a parameter
to control cubic crystalline electric field effect, one orbital is itinerant,
while other two are localized. Due to the competition between itinerant and
localized natures, we obtain orbital ordering pattern which is sensitive to
, leading to a characteristic change of quadrupole state
into an incommensurate structure. At , all the three orbitals are
degenerate, but we observe a peak at in quadrupole
correlation, indicating a ferro-orbital state, and the peak at in
dipole correlation, suggesting an antiferromagnetic state. We
also discuss the effect of octupole on magnetic anisotropy.Comment: 4 pages, 3 figures, Proceedings of ASR-WYP-2005 (September 27-29,
2005, Tokai
Fulde-Ferrell-Larkin-Ovchinnikov State in the absence of a Magnetic Field
We propose that in a system with pocket Fermi surfaces, a pairing state with
a finite total momentum q_tot like the Fulde-Ferrell-Larkin-Ovchinnikov state
can be stabilized even without a magnetic field. When a pair is composed of
electrons on a pocket Fermi surface whose center is not located at Gamma point,
the pair inevitably has finite q_tot. To investigate this possibility, we
consider a two-orbital model on a square lattice that can realize pocket Fermi
surfaces and we apply fluctuation exchange approximation. Then, by changing the
electron number n per site, we indeed find that such superconducting states
with finite q_tot are stabilized when the system has pocket Fermi surfaces.Comment: 4 pages, 5 figure
A new view of the spin echo diffusive diffraction on porous structures
Analysis with the characteristic functional of stochastic motion is used for
the gradient spin echo measurement of restricted motion to clarify details of
the diffraction-like effect in a porous structure. It gives the diffusive
diffraction as an interference of spin phase shifts due to the back-flow of
spins bouncing at the boundaries, when mean displacement of scattered spins is
equal to the spin phase grating prepared by applied magnetic field gradients.
The diffraction patterns convey information about morphology of the surrounding
media at times long enough that opposite boundaries are restricting
displacements. The method explains the dependence of diffraction on the time
and width of gradient pulses, as observed at the experiments and the
simulations. It also enlightens the analysis of transport properties by the
spin echo, particularly in systems, where the motion is restricted by structure
or configuration
Effective Crystalline Electric Field Potential in a j-j Coupling Scheme
We propose an effective model on the basis of a - coupling scheme to
describe local -electron states for realistic values of Coulomb interaction
and spin-orbit coupling , for future development of microscopic
theory of magnetism and superconductivity in -electron systems, where
is the number of local electrons. The effective model is systematically
constructed by including the effect of a crystalline electric field (CEF)
potential in the perturbation expansion in terms of . In this paper,
we collect all the terms up to the first order of . Solving the
effective model, we show the results of the CEF states for each case of
=25 with symmetry in comparison with those of the Stevens
Hamiltonian for the weak CEF. In particular, we carefully discuss the CEF
energy levels in an intermediate coupling region with in the order
of 0.1 corresponding to actual -electron materials between the and
- coupling schemes. Note that the relevant energy scale of is the
Hund's rule interaction. It is found that the CEF energy levels in the
intermediate coupling region can be quantitatively reproduced by our modified
- coupling scheme, when we correctly take into account the corrections in
the order of in addition to the CEF terms and Coulomb interactions
which remain in the limit of =. As an application of the
modified - coupling scheme, we discuss the CEF energy levels of filled
skutterudites with symmetry.Comment: 12 pages, 7 figures. Typeset with jpsj2.cl
Intrabeam Scattering Analysis of ATF Beam Measurements
At the Accelerator Test Facility (ATF) at KEK intrabeam scattering (IBS) is a
strong effect for an electron machine. It is an effect that couples all
dimensions of the beam, and in April 2000, over a short period of time, all
dimensions were measured as functions of current. In this report we derive a
simple relation for the growth rates of emittances due to IBS. We apply the
theories of Bjorken-Mtingwa, Piwinski, and a formula due to Raubenheimer to the
ATF parameters, and find that the results all agree (if in Piwinski's formalism
we replace the dispersion squared over beta by the dispersion invariant).
Finally, we compare theory, including the effect of potential well bunch
lengthening, with the April 2000 measurements, and find reasonably good
agreement in the energy spread and horizontal emittance dependence on current.
The vertical emittance measurement, however, implies that either: there is
error in the measurement (equivalent to an introduction of 0.6% x-y coupling
error), or the effect of intrabeam scattering is stronger than predicted (35%
stronger in growth rates).Comment: 4 pages, 3 figures, Presented at IEEE Particle Accelerator Conferenc
Quadrupole Susceptibility of Gd-Based Filled Skutterudite Compounds
It is shown that quadrupole susceptibility can be detected in Gd compounds
contrary to our textbook knowledge that Gd ion induces pure spin moment
due to the Hund's rules in an coupling scheme. The ground-state multiplet
of Gd is always characterized by =7/2, where denotes total
angular momentum, but in a - coupling scheme, one electron in =7/2
octet carries quadrupole moment, while other six electrons fully occupy =5/2
sextet, where denotes one-electron total angular momentum. For realistic
values of Coulomb interaction and spin-orbit coupling, the ground-state
wavefunction is found to contain significant amount of the - coupling
component. From the evaluation of quadrupole susceptibility in a simple
mean-field approximation, we point out a possibility to detect the softening of
elastic constant in Gd-based filled skutterudites.Comment: 8 pages, 4 figure
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