Condensed Matter Seminar Series
A Monte Carlo Study of Spatially Anisotropic Spin-1/2 Heisenberg Models
Tuesday March 23, 3:30pm,
Room 298, Physics Building
Heisenberg models have been studied in great detail, because of their
phenomenological as well as theoretical importance. For instance, the
discovery of high temperature (high $T_c$) superconductivity in the
materials has triggered vigorous research investigation on
spin-1/2 Heisenberg-type models, which are argued and believed to be
correct models for the undoped precursors of high $T_c$ cuprates.
On the other hand, despite being well-studied, several recent Monte
investigations of spatially anisotropic Heisenberg models have led to
unexpected results. For example, numerical evidence shows that the
anisotropic spin-1/2 Heisenberg model with a staggered arrangement of
antiferromagnetic couplings may belong to a new universality class,
in contradiction to the theoretical $O(3)$ universality prediction.
Further, Monte Carlo data indicates an unconventional behavior for
the transition of the spin-1/2 Heisenberg model with different
couplings in the 1- and 2-spatial directions
to its 1-D limit, namely decoupled Heisenberg chains. Because of these
surprising results, we use first principles Monte Carlo simulations to
investigate these two spatially anisotropic spin-1/2 Heisenberg models.
In particular, by employing the idea of fixing the ratio of
spatial winding number squareds in the simulations, we show a
clear O(3) universality class signal
for the first model. We provide a convincing evidence for
an unconventional transition of the second model to its 1-D limit as
Specifically the critical exponent $\nu$ obtained from the simulations
is given by $\nu = 0.92(3)$ which is not known in the literature.
Host: Shailesh Chandrasekharan