3,255 research outputs found
Exotic disordered phases in the quantum model on the honeycomb lattice
We study the ground-state phase diagram of the frustrated quantum
Heisenberg antiferromagnet on the honeycomb lattice using a mean field approach
in terms of the Schwinger boson representation of the spin operators. We
present results for the ground-state energy, local magnetization, energy gap
and spin-spin correlations. The system shows magnetic long range order for
(N\'eel) and (spiral). In the intermediate region, we find two magnetically disordered
phases: a gapped spin liquid phase which shows short-range N\'eel correlations
, and a lattice nematic phase
, which is magnetically disordered
but breaks lattice rotational symmetry. The errors in the values of the phase
boundaries which are implicit in the number of significant figures quoted,
correspond purely to the error in the extrapolation of our finite-size results
to the thermodynamic limit.Comment: 11 pages, 9 figures, to appear in Phys. Rev.
Dimerized ground states in spin-S frustrated systems
We study a family of frustrated anti-ferromagnetic spin- systems with a
fully dimerized ground state. This state can be exactly obtained without the
need to include any additional three-body interaction in the model. The
simplest members of the family can be used as a building block to generate more
complex geometries like spin tubes with a fully dimerized ground state. After
present some numerical results about the phase diagram of these systems, we
show that the ground state is robust against the inclusion of weak disorder in
the couplings as well as several kinds of perturbations, allowing to study some
other interesting models as a perturbative expansion of the exact one. A
discussion on how to determine the dimerization region in terms of quantum
information estimators is also presented. Finally, we explore the relation of
these results with a the case of the a 4-leg spin tube which recently was
proposed as the model for the description of the compound
CuClDCSO, delimiting the region of the parameter space
where this model presents dimerization in its ground state.Comment: 10 pages, 9 figure
Phase diagram study of a dimerized spin-S zig-zag ladder
The phase diagram of a frustrated spin- zig-zag ladder is studied through
different numerical and analytical methods. We show that for arbitrary ,
there is a family of Hamiltonians for which a fully-dimerized state is an exact
ground state, being the Majumdar-Ghosh point a particular member of the family.
We show that the system presents a transition between a dimerized phase to a
N\'eel-like phase for , and spiral phases can appear for large . The
phase diagram is characterized by means of a generalization of the usual Mean
Field Approximation (MFA). The novelty in the present implementation is to
consider the strongest coupled sites as the unit cell. The gap and the
excitation spectrum is analyzed through the Random Phase Approximation (RPA).
Also, a perturbative treatment to obtain the critical points is discussed.
Comparisons of the results with numerical methods like DMRG are also presented.Comment: 14 pages, 6 figures. Some typos were corrected, and notation was
clarifie
Quantum phases in the frustrated Heisenberg model on the bilayer honeycomb lattice
We use a combination of analytical and numerical techniques to study the
phase diagram of the frustrated Heisenberg model on the bilayer honeycomb
lattice. Using the Schwinger boson description of the spin operators followed
by a mean field decoupling, the magnetic phase diagram is studied as a function
of the frustration coupling and the interlayer coupling .
The presence of both magnetically ordered and disordered phases is
investigated by means of the evaluation of ground-state energy, spin gap, local
magnetization and spin-spin correlations. We observe a phase with a spin gap
and short range N\'eel correlations that survives for non-zero
next-nearest-neighbor interaction and interlayer coupling. Furthermore, we
detect signatures of a reentrant behavior in the melting of N\'eel phase and
symmetry restoring when the system undergoes a transition from an on-layer
nematic valence bond crystal phase to an interlayer valence bond crystal phase.
We complement our work with exact diagonalization on small clusters and
dimer-series expansion calculations, together with a linear spin wave approach
to study the phase diagram as a function of the spin , the frustration and
the interlayer couplings.Comment: 10 pages, 9 figure
Quantum phase diagram of a frustrated antiferromagnet on the bilayer honeycomb lattice
We study the spin-1/2 Heisenberg antiferromagnet on a bilayer honeycomb
lattice including interlayer frustration. Using a set of complementary
approaches, namely Schwinger bosons, dimer series expansion, bond operators,
and exact diagonalization, we map out the quantum phase diagram. Analyzing
ground state energies and elementary excitation spectra, we find four distinct
phases, corresponding to three collinear magnetic long range ordered states,
and one quantum disordered interlayer dimer phase. We detail, that the latter
phase is adiabatically connected to an "exact" singlet product ground state of
the the bilayer which exists along a line of maximum interlayer frustration.
The order within the remaining three phases will be clarified.Comment: 12 pages, 12 figure
Influence of shear lag on the collapse of wide-flange girders
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