2,618 research outputs found
Spin excitations and thermodynamics of the t-J model on the honeycomb lattice
We present a spin-rotation-invariant Green-function theory for the dynamic
spin susceptibility in the spin-1/2 antiferromagnetic t-J Heisenberg model on
the honeycomb lattice. Employing a generalized mean-field approximation for
arbitrary temperatures and hole dopings, the electronic spectrum of
excitations, the spin-excitation spectrum and thermodynamic quantities
(two-spin correlation functions, staggered magnetization, magnetic
susceptibility, correlation length) are calculated by solving a coupled system
of self-consistency equations for the correlation functions. The temperature
and doping dependence of the magnetic (uniform static) susceptibility is
ascribed to antiferromagnetic short-range order. Our results on the doping
dependencies of the magnetization and susceptibility are analyzed in comparison
with previous results for the t_J model on the square lattice.Comment: 9 pages, 7 figures, submitted to European Physical Journal B. arXiv
admin note: text overlap with arXiv:1703.0839
Dynamic spin susceptibility of superconducting cuprates: A microscopic theory of the magnetic resonance mode
A microscopic theory of the dynamic spin susceptibility (DSS) in the
superconducting state within the t-J model is presented. It is based on an
exact representation for the DSS obtained by applying the Mori-type projection
technique for the relaxation function in terms of Hubbard operators. The static
spin susceptibility is evaluated by a sum-rule-conserving generalized
mean-field approximation, while the self-energy is calculated in the
mode-coupling approximation. The spectrum of spin excitations is studied in the
underdoped and optimally doped regions. The DSS reveals a resonance mode (RM)
at the antiferromagnetic wave vector Q = \pi(1,1) at low temperatures due to a
strong suppression of the damping of spin excitations. This is explained by an
involvement of spin excitations in the decay process besides the particle-hole
continuum usually considered in random-phase-type approximations. The spin gap
in the spin-excitation spectrum at Q plays a dominant role in limiting the
decay in comparison with the superconducting gap which results in the
observation of the RM even above in the underdoped region. A good
agreement with inelastic neutron-scattering experiments on the RM in YBCO
compounds is found.Comment: 15 pages, 20 figures, references adde
Electroproduction of tensor mesons in QCD
Due to multiple possible polarizations hard exclusive production of tensor
mesons by virtual photons or in heavy meson decays offers interesting
possibilities to study the helicity structure of the underlying short-distance
process. Motivated by the first measurement of the transition form factor
at large momentum transfers by the BELLE
collaboration we present an improved QCD analysis of this reaction in the
framework of collinear factorization including contributions of twist-three
quark-antiquark-gluon operators and an estimate of soft end-point corrections
using light-cone sum rules. The results appear to be in a very good agreement
with the data, in particular the predicted scaling behavior is reproduced in
all cases.Comment: 27 pages, 5 figure
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