1,751 research outputs found
Quasiperiodic Hubbard chains
Low energy properties of half-filled Fibonacci Hubbard models are studied by
weak coupling renormalization group and density matrix renormalization group
method. In the case of diagonal modulation, weak Coulomb repulsion is
irrelevant and the system behaves as a free Fibonacci chain, while for strong
Coulomb repulsion, the charge sector is a Mott insulator and the spin sector
behaves as a uniform Heisenberg antiferromagnetic chain. The off-diagonal
modulation always drives the charge sector to a Mott insulator and the spin
sector to a Fibonacci antiferromagnetic Heisenberg chain.Comment: 4 pages, 4 figures; Final version to appear in Phys. Rev. Let
Magnetization plateaus in antiferromagnetic-(ferromagnetic)_{n} polymerized S=1/2 XXZ chains
The plateau-non-plateau transition in the
antiferromagnetic-(ferromagnetic) polymerized XXZ chains under
the magnetic field is investigated. The universality class of this transition
belongs to the Brezinskii-Kosterlitz-Thouless (BKT) type. The critical points
are determined by level spectroscopy analysis of the numerical diagonalization
data for where is the size of a unit cell.
It is found that the critical strength of ferromagnetic coupling decreases with
for small but increases for larger enough . It is also found that
the plateau for large is wide enough for moderate values of exchange
coupling so that it should be easily observed experimentally. This is in
contrast to the plateaus for chains which are narrow for a wide range
of exchange coupling even away from the critical point
Density Matrix Renormalization Group Study of the Haldane Phase in Random One-Dimensional Antiferromagnets
It is conjectured that the Haldane phase of the S=1 antiferromagnetic
Heisenberg chain and the ferromagnetic-antiferromagnetic alternating
Heisenberg chain is stable against any strength of randomness, because of
imposed breakdown of translational symmetry. This conjecture is confirmed by
the density matrix renormalization group calculation of the string order
parameter and the energy gap distribution.Comment: 4 Pages, 7 figures; Considerable revisions are made in abstract and
main text. Final accepted versio
EXAFS Study on Local Structure of Iron Crystal by the Use of Asymmetrical Monochromator and PSPC
The EXAFS spectroscopy equipment constructed from an asymmetrical cut flat monochromator and PSPC is applied to the structural determination of pure α-iron which has small difference (0.038nm) in the first and second nearest neighbour distance. The efficiency of the curve fitting method for the two shell model of known structure material (α-iron) is discussed, in addition to describing the details of the experimental procedure of our new type of spectrometer and of the EXAFS data analysis
Critical Properties of the transition between the Haldane phase and the large-D phase of the spin-1/2 ferromagnetic-antiferromagnetic Heisenberg chain with on-site anisotropy"
We analytically study the ground-state quantum phase transition between the
Haldane phase and the large- (LD) phase of the
ferromagnetic-antiferromagnetic alternating Heisenberg chain with on-site
anisotropy. We transform this model into a generalized version of the
alternating antiferromagnetic Heisenberg model with anisotropy. In the
transformed model, the competition between the transverse and longitudinal bond
alternations yields the Haldane-LD transition. Using the bosonization method,
we show that the critical exponents vary continuously on the Haldane-LD
boundary. Our scaling relations between critical exponents very well explains
the numerical results by Hida.Comment: text 12 pages (Plain TeX), LaTeX sourse files of a table and a figure
on reques
Computing automorphic forms on Shimura curves over fields with arbitrary class number
We extend methods of Greenberg and the author to compute in the cohomology of
a Shimura curve defined over a totally real field with arbitrary class number.
Via the Jacquet-Langlands correspondence, we thereby compute systems of Hecke
eigenvalues associated to Hilbert modular forms of arbitrary level over a
totally real field of odd degree. We conclude with two examples which
illustrate the effectiveness of our algorithms.Comment: 15 pages; final submission to ANTS I
Interacting Boson Theory of the Magnetization Process of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain
The low temperature magnetization process of the
ferromagnetic-antiferromagnetic Heisenberg chain is studied using the
interacting boson approximation. In the low field regime and near the
saturation field, the spin wave excitations are approximated by the
function boson gas for which the Bethe ansatz solution is available. The finite
temperature properties are calculated by solving the integral equation
numerically. The comparison is made with Monte Carlo calculation and the limit
of the applicability of the present approximation is discussed.Comment: 4 pages, 7 figure
The antiferromagnetic order in an F-AF random alternating quantum spin chain : (CH_3)_2 CHNH_3 Cu(Cl_x Br_{1-x})_3
A possibility of the uniform antiferromagnetic order is pointed out in an
S=1/2 ferromagnetic (F) - antiferromagnetic (AF) random alternating Heisenberg
quantum spin chain compound: (CH_3)_2 CHNH_3 Cu(Cl_x Br_{1-x})_3. The system
possesses the bond alternation of strong random bonds that take +/- 2J and weak
uniform AF bonds of -J. In the pure concentration limits, the model reduces to
the AF-AF alternation chain at x=0 and to the F-AF alternation chain at x=1.
The nonequilibrium relaxation of large-scale quantum Monte Carlo simulations
exhibits critical behaviors of the uniform AF order in the intermediate
concentration region, which explains the experimental observation of the
magnetic phase transition. The present results suggest that the uniform AF
order may survive even in the presence of the randomly located ferromagnetic
bonds.Comment: 4 pages, 3 figure
Density Matrix Renormalization Group Study of the S=1/2 Anisotropic Antiferromagnetic Heisenberg Chains with Quasiperiodic Exchange Modulation
The low energy behavior of the S=1/2 antiferromagnetic XY-like XXZ chains
with precious mean quasiperiodic exchange modulation is studied by the density
matrix renormalization group method. It is found that the energy gap of the
chain with length N scales as with nonuniversal exponent
if the Ising component of the exhange coupling is antiferromagnetic.
This behavior is expected to be the characteristic feature of the quantum spin
chains with relevant aperiodicity. This is in contrast to the XY chain for
which the precious mean exchange modulation is marginal and the gap scales as
. On the contrary, it is also verified that the energy gap scales as
if the Ising component of the exhange coupling is ferromagnetic. Our
results are not only consistent with the recent bosonization analysis of Vidal,
Mouhanna and Giamarchi but also clarify the nature of the strong coupling
regime which is inaccesssible by the bosonization approach.Comment: 8 pages, 15 figures, 1 table; Proceedings of the workshop 'Frontiers
in Magnetism', Kyoto, Oct. 199
Excitation Spectrum of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain:
The natural explanation of the excitation spectrum of the spin-1
antiferromagnetic Heisenberg chain is given from the viewpoint of the spin-1/2
ferromagnetic-antiferromagnetic alternating Heisenberg chain. The energy
spectrum of the latter is calculated with fixed momentum by numerical
diagonalization of finite size systems. It consists of a branch of propagating
triplet pair (triplet wave) and the continuum of multiple triplet waves for
weak ferromagnetic coupling. As the ferromagnetic coupling increases, the
triplet wave branch is absorbed in the continuum for small , reproducing the
characteristics of the spin-1 antiferromagnetic Heisenberg chain.Comment: 12 Pages REVTEX, Postscript file for the figures included.
SKPH-94-C00
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