D. Shubashree | Searcharxiv

arXiv1999

A hidden Goldstone mechanism in the Kagomé lattice antiferromagnet

In this paper, we study the phases of the Heisenberg model on the \kagome lattice with antiferromagnetic nearest neighbour coupling $J_1$ and ferromagnetic next neighbour coupling $J_2$. Analysing the long wavelength, low energy effective action that describes this model, we arrive at the phase diagram as a function of $χ= \frac{J_2}{J_1} $. The interesting part of this phase diagram is that for small $χ$, which includes $χ=0$, there is a phase with no long range spin order and with gapless and spin zero low lying excitations. We discuss our results in the context of earlier, numerical and experimental work.

cond-mat.str-el↗

arXiv1997

Field Theory of Quantum Antiferromagnets : From the Triangular to the Kagome Lattice

We analyse a family of models, that interpolates between the Triangular lattice antiferromagnet (TLAF) and the Kagome lattice antiferromagnet (KLAF). We identify the field theories governing the low energy, long wavelength physics of these models. Near the TLAF the low energy field theory is a nonlinear sigma model of a SO(3) group valued field. The SO(3) symmetry of the spin system is enhanced to a $SO(3)_R \times SO(2)_L$ symmetry in the field theory. Near the KLAF other modes become important and the field takes values in $SO(3) \times S_2$. We analyse this field theory and show that it admits a novel phase in which the $SO(3)_R$ spin symmetry is unbroken and the $SO(2)_L$ symmetry is broken. We propose this as a possible mechanism by which a gapless excitation can exist in the KLAF without breaking the spin rotation symmetry.

cond-mat↗