Field-induced spontaneous magnon decay in a spin-1/2 coupled two-leg ladder antiferromagnet C9H18N2CuBr4 with small Ising anisotropy

We present the high-resolution neutron scattering study in magnetic fields applied perpendicular to an easy-axis (Ising type) on the $S=$1/2 coupled two-leg ladder antiferromagnet (dimethylammonium)(3,5-dimethylpyridinium)CuBr$_{\mathrm{4}}$. At finite fields, the magnetic structure becomes noncollinear canted and the observed intriguing spontaneous magnon decays over a large region of Brillouin Zone in the excitation spectra can be well explained by the mechanism where the process of one-magnon decays into two-magnon continuum is kinematically allowed [1]. [1] M. E. Zhitomirsky and A. L. Chernyshev, Rev. Mod. Phys. \textbf{85}, 219 (2013).