Magnetic spiral order in the square-lattice spin system (CuBr)Sr${}_2$Nb${}_3$O${}_{10}$

Abstract

We address quantum spin helical states in the strongly frustrated Heisenberg model. Contrary to conventional Dzyaloshinskii-Moriya approach we show that such states appear without central symmetry breaking. As an example, we demonstrate that the magnetic and thermodynamic properties of the quasi-two-dimensional square-lattice compound $(\mathrm{CuBr})\mathrm{S}{\mathrm{r}}_2\mathrm{N}{\mathrm{b}}_3{\mathrm{O}}_{10}$ can be interpreted within 2D $S=1/2$ $J_1-J_2-J_3$ Heisenberg model. In this compound neutron experiment indicates helical spin order while central symmetry does hold.