Pathology Of Schwinger Boson Mean Field Theory Above Two Dimension

Max A. Lohe, C. A. Hurst

Tai Kai Ng

The origin and properties of the S=1/2 end states in S=1 open spin chains is explained within the framework of Schwinger-boson mean-field theory. Moreover, we show that in two dimensions (square lattice), corresponding edge states exist with structures depending on spin magnitude S.

Qiu Zhang, Tao Li

We find that the Schwinger boson mean field theory (SBMFT) supplemented with Gutzwiller projection provides an exceedingly accurate description for the ground state of the spin-12triangular lattice antiferromagnetic Heisenberg model (spin-12TLHAF). However, we find the SBMFT fails even qualitatively in the description of the dynamical behavior of the system. In particular, the SBMFT fails to predict the Goldstone mode in the magnetic ordered phase. We show that the coherent peak in the two-spinon continuum in the presence of spinon condensate should not be interpreted as a magnon mode. The SBMFT also predicts incorrectly a gapless longitudinal spin fluctuation mode in the magnetic ordered phase. We show that these failures are related to the following facts: (1) spinon condensation fails to provide a consistent description of the order parameter manifold of the 120 degree ordered phase. (2) There lacks in the SBMFT the coupling between the uncondensed spinon and the spinon condensate, which breaks both the spin rotational and the translational symmetry. (3) There lacks in the SBMFT the rigidity that is related to the no double occupancy constraint on the spinon system. We show that such failures of the SBMFT is neither restricted to the spin-12TLHAF nor to the magnetic ordered phase. We proposed a generalized SBMFT to resolve the first two issues and a new formalism to address the third issue.

Antônio Sérgio Teixeira Pires

Shivam Ghosh, Hitesh J. Changlani, Christopher L. Henley

The authors study the diluted spin-half Heisenberg model near the percolation threshold using Schwinger boson mean field theory (SBMFT). They show how SBMFT predicts the emergence of effective local spin degrees of freedom. They demonstrate that SBMFT applied to dilute spin systems is qualitatively accurate by also performing DMRG computations.