Schwinger-boson approach to the kagome antiferromagnet with Dzyaloshinskii-Moriya interactions: Phase diagram and dynamical structure factors

Abstract

We have obtained the zero-temperature phase diagram of the kagom\'e antiferromagnet with Dzyaloshinskii-Moriya interactions in Schwinger-boson mean-field theory. We find quantum phase transitions (first or second order) between different topological spin-liquid and N\'eel-ordered phases (either the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ state or the so-called $\mathbf{Q}=0$ state). In the regime of small Schwinger-boson density, the results bear some resemblances with exact diagonalization results and we briefly discuss some issues of the mean-field treatment. We calculate the equal-time structure factor (and its angular average to allow for a direct comparison with experiments on powder samples), which extends earlier work on the classical kagom\'e to the quantum regime. We also discuss the dynamical structure factors of the topological spin-liquid and the N\'eel-ordered phases.