86,956 research outputs found
Family of exactly solvable models with an ultimative quantum paramagnetic ground state
We present a family of two-dimensional frustrated quantum magnets solely
based on pure nearest-neighbor Heisenberg interactions which can be solved
quasi-exactly. All lattices are constructed in terms of frustrated quantum
cages containing a chiral degree of freedom protected by frustration. The
ground states of these models are dubbed ultimate quantum paramagnets and
exhibit an extensive entropy at zero temperature. We discuss the unusual and
extensively degenerate excitations in such phases. Implications for
thermodynamic properties as well as for decoherence free quantum computation
are discussed
Period preserving nonisospectral flows and the moduli space of periodic solutions of soliton equations
Flows on the moduli space of the algebraic Riemann surfaces, preserving the
periods of the corresponding solutions of the soliton equations are studied. We
show that these flows are gradient with respect to some indefinite symmetric
flat metric arising in the Hamiltonian theory of the Whitham equations. The
functions generating these flows are conserved quantities for all the equations
simultaneously. We show that for 1+1 systems these flows can be imbedded in a
larger system of ordinary nonlinear differential equations with a rational
right-hand side. Finally these flows are used to give a complete description of
the moduli space of algebraic Riemann surfaces corresponding to periodic
solutions of the nonlinear Schr\"odinger equation.Comment: 35 pages, LaTex. Macros file elsart.sty is used (it was submitted by
the authors to [email protected] library macroses),e-mail:
[email protected], e-mail:[email protected]
Closed curves in R^3: a characterization in terms of curvature and torsion, the Hasimoto map and periodic solutions of the Filament Equation
If a curve in R^3 is closed, then the curvature and the torsion are periodic
functions satisfying some additional constraints. We show that these
constraints can be naturally formulated in terms of the spectral problem for a
2x2 matrix differential operator. This operator arose in the theory of the
self-focusing Nonlinear Schrodinger Equation.
A simple spectral characterization of Bloch varieties generating periodic
solutions of the Filament Equation is obtained. We show that the method of
isoperiodic deformations suggested earlier by the authors for constructing
periodic solutions of soliton equations can be naturally applied to the
Filament Equation.Comment: LaTeX, 27 pages, macros "amssym.def" use
Unifying Magnons and Triplons in Stripe-Ordered Cuprate Superconductors
Based on a two-dimensional model of coupled two-leg spin ladders, we derive a
unified picture of recent neutron scattering data of stripe-ordered
La_(15/8)Ba_(1/8)CuO_4, namely of the low-energy magnons around the
superstructure satellites and of the triplon excitations at higher energies.
The resonance peak at the antiferromagnetic wave vector Q_AF in the
stripe-ordered phase corresponds to a saddle point in the dispersion of the
magnetic excitations. Quantitative agreement with the neutron data is obtained
for J= 130-160 meV and J_cyc/J = 0.2-0.25.Comment: 4 pages, 4 figures included updated version taking new data into
account; factor in spectral weight corrected; Figs. 2 and 4 change
The fate of orbitons coupled to phonons
The key feature of an orbital wave or orbiton is a significant dispersion,
which arises from exchange interactions between orbitals on distinct sites. We
study the effect of a coupling between orbitons and phonons in one dimension
using continuous unitary transformations (CUTs). Already for intermediate
values of the coupling, the orbiton band width is strongly reduced and the
spectral density is dominated by an orbiton-phonon continuum. However, we find
sharp features within the continuum and an orbiton-phonon anti-bound state
above. Both show a significant dispersion and should be observable
experimentally.Comment: 7 pages, 7 figures; strongly enlarged, comprehensive revised version
according to the referees' suggestions, in pres
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