10 research outputs found
Low-energy parameters and spin gap of a frustrated spin- Heisenberg antiferromagnet with on the honeycomb lattice
The coupled cluster method is implemented at high orders of approximation to
investigate the zero-temperature phase diagram of the frustrated
spin- ---- antiferromagnet on the honeycomb lattice.
The system has isotropic Heisenberg interactions of strength ,
and between nearest-neighbour, next-nearest-neighbour and
next-next-nearest-neighbour pairs of spins, respectively. We study it in the
case , in the window
that contains the classical tricritical point (at ) of maximal frustration, appropriate to the limiting value of the spin quantum number. We present results for the magnetic
order parameter , the triplet spin gap , the spin stiffness
and the zero-field transverse magnetic susceptibility for the
two collinear quasiclassical antiferromagnetic (AFM) phases with N\'{e}el and
striped order, respectively. Results for and are given for the
three cases , and , while those for
and are given for the two cases and . On
the basis of all these results we find that the spin- and spin-1
models both have an intermediate paramagnetic phase, with no discernible
magnetic long-range order, between the two AFM phases in their phase
diagrams, while for there is a direct transition between them. Accurate
values are found for all of the associated quantum critical points. While the
results also provide strong evidence for the intermediate phase being gapped
for the case , they are less conclusive for the case . On
balance however, at least the transition in the latter case at the striped
phase boundary seems to be to a gapped intermediate state
The effect of four-spin exchanges on the honeycomb lattice diagram phase of S=3/2 J1-J2 Antiferromagnetic Heisenberg model
In this study, the effect of four-spin exchanges between the nearest and next nearest neighbor spins of honeycomb lattice on the phase diagram of S=3/2 antiferomagnetic Heisenberg model is considered with two-spin exchanges between the nearest and next nearest neighbor spins. Firstly, the method is investigated with classical phase diagram. In classical phase diagram, in addition to Neel order, classical degeneracy is also seen. The existance of this phase in diagram phase is important because of the probability of the existence of quantum spin liquid in this region for such amount of interaction. To investigate the effect of quantum fluctuation on the stability of the obtained classical phase diagram, linear spin wave theory has been used. Obtained results show that in classical degeneracy regime, the quantum fluctuations cause the order by disorder in the spin system and the ground state is ordere