828 research outputs found
Dynamical properties of S=1 bond-alternating Heisenberg chains in transverse magnetic fields
We calculate dynamical structure factors of the S=1 bond-alternating
Heisenberg chain with a single-ion anisotropy in transverse magnetic fields,
using a continued fraction method based on the Lanczos algorithm. In the
Haldane-gap phase and the dimer phase, dynamical structure factors show
characteristic field dependence. Possible interpretations are discussed. The
numerical results are in qualitative agreement with recent results for
inelastic neutron-scattering experiments on the S=1 bond-alternating
Heisenberg-chain compound and the
S=1 Haldane-gap compound in
transverse magnetic fields.Comment: 7 pages, 6 figure
Existence of Saturated Ferromagnetic and Spiral States in 1D Lieb-Ferrimagnetic Models away from Half-Filling
In order to study conditions for the appearance of ferromagnetism in a wide
filling region, we investigate numerically three types of one-dimensional
Lieb-ferrimagnetic Hubbard models: a periodic diamond (PD) chain, a periodic
alternately-attached leg (PAAL) chain and an open diamond (OD) chain. All of
these models have a flat band (or equivalently, degenerate single-electron
eigenvalues). The PD and OD chains commonly have a local-loop structure.
Nagaoka's theorem holds only in the PD chain. At half-filling, it have been
rigorously proven that all of these models are ferrimagnet. Away from
half-filling, however, quite different magnetic properties are found. In the
fillings 1/3< rho_e <1/2, the ground state of the PD chain for a
infinitely-large U is the extended ferromagnetic state, that is, the saturated
ferromagnetic state or the spiral state for odd or even number of electrons,
respectively. In the PAAL chain, on the other hand, there is no magnetic order.
Thus, the flat band is found to be not a sufficient condition of the extended
ferromagnetic state. We find, moreover, that the saturated ferromagnetism
appears in the OD chain, although the Nagaoka theorem does not hold on this
chain. This indicates that the local-loop structure plays an important role on
the appearance of the extended ferromagnetic state.Comment: 4 pages, 4 figures, 2 tables. to be published in J. Phys. Soc. Jpn.
Vol. 68 No.
Adiabatic connection between the RVB State and the ground state of the half filled periodic Anderson model
A one-parameter family of models that interpolates between the periodic
Anderson model with infinite repulsion at half-filling and a model whose ground
state is exactly the Resonating-Valence-Bond state is studied. It is shown
numerically that the excitation gap does not collapse. Therefore the ground
states of the two models are adiabatically connected.Comment: 6 pages, 3 figures Revte
Quantum Multibaker Maps: Extreme Quantum Regime
We introduce a family of models for quantum mechanical, one-dimensional
random walks, called quantum multibaker maps (QMB). These are Weyl
quantizations of the classical multibaker models previously considered by
Gaspard, Tasaki and others. Depending on the properties of the phases
parametrizing the quantization, we consider only two classes of the QMB maps:
uniform and random. Uniform QMB maps are characterized by phases which are the
same in every unit cell of the multibaker chain. Random QMB maps have phases
that vary randomly from unit cell to unit cell. The eigenstates in the former
case are extended while in the latter they are localized. In the uniform case
and for large , analytic solutions can be obtained for the time
dependent quantum states for periodic chains and for open chains with absorbing
boundary conditions. Steady state solutions and the properties of the
relaxation to a steady state for a uniform QMB chain in contact with
``particle'' reservoirs can also be described analytically. The analytical
results are consistent with, and confirmed by, results obtained from numerical
methods. We report here results for the deep quantum regime (large ) of
the uniform QMB, as well as some results for the random QMB. We leave the
moderate and small results as well as further consideration of the
other versions of the QMB for further publications.Comment: 17 pages, referee's and editor's comments addresse
Autonomous Attitude Determination System (AADS). Volume 1: System description
Information necessary to understand the Autonomous Attitude Determination System (AADS) is presented. Topics include AADS requirements, program structure, algorithms, and system generation and execution
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