8,705 research outputs found
Picard-Fuchs Equations and Whitham Hierarchy in N=2 Supersymmetric SU(r+1) Yang-Mills Theory
In general, Whitham dynamics involves infinitely many parameters called
Whitham times, but in the context of N=2 supersymmetric Yang-Mills theory it
can be regarded as a finite system by restricting the number of Whitham times
appropriately. For example, in the case of SU(r+1) gauge theory without
hypermultiplets, there are r Whitham times and they play an essential role in
the theory. In this situation, the generating meromorphic 1-form of the Whitham
hierarchy on Seiberg-Witten curve is represented by a finite linear combination
of meromorphic 1-forms associated with these Whitham times, but it turns out
that there are various differential relations among these differentials. Since
these relations can be written only in terms of the Seiberg-Witten 1-form,
their consistency conditions are found to give the Picard-Fuchs equations for
the Seiberg-Witten periods.Comment: to be published in J. Math. Phys, revtex, 14 page
Chemical potential shift in La(1-x)Sr(x)MnO(3): Photoemission test of the phase separation scenario
We have studied the chemical potential shift in La(1-x)Sr(x)MnO(3) as a
function of doped hole concentration by core-level x-ray photoemission. The
shift is monotonous, which means that there is no electronic phase separation
on a macroscopic scale, whereas it is consistent with the nano-meter scale
cluster formation induced by chemical disorder. Comparison of the observed
shift with the shift deduced from the electronic specific heat indicates that
hole doping in La(1-x)Sr(x)MnO(3) is well described by the rigid-band picture.
In particular no mass enhancement toward the metal-insulator boundary was
implied by the chemical potential shift, consistent with the electronic
specific heat data.Comment: 7 pages, 3 figures, to be published in Europhysics Letter
Ground states with cluster structures in a frustrated Heisenberg chain
We examine the ground state of a Heisenberg model with arbitrary spin S on a
one-dimensional lattice composed of diamond-shaped units. A unit includes two
types of antiferromagnetic exchange interactions which frustrate each other.
The system undergoes phase changes when the ratio between the
exchange parameters varies. In some phases, strong frustration leads to larger
local structures or clusters of spins than a dimer. We prove for arbitrary S
that there exists a phase with four-spin cluster states, which was previously
found numerically for a special value of in the S=1/2 case. For S=1/2
we show that there are three ground state phases and determine their
boundaries.Comment: 4 pages, uses revtex.sty, 2 figures available on request from
[email protected], to be published in J. Phys.: Cond. Mat
Spin Gap of Two-Dimensional Antiferromagnet Representing CaVO
We examined a two-dimensional Heisenberg model with two kinds of exchange
energies, and . This model describes localized spins at vanadium
ions in a layer of CaVO, for which a spin gap is found by a recent
experiment. Comparing the high temperature expansion of the magnetic
susceptibility to experimental data, we determined the exchange energies as
610 K and 150 K. By the numerical diagonalization we
estimated the spin gap as 120 K, which consists
with the experimental value 107 K. Frustration by finite enhances the
spin gap.Comment: 12 pages of LaTex, 4 figures availavule upon reques
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