Neutron Scattering Study on the Spin-1/2 Triangular-Lattice Antiferromagnet Ba$_{3}$CoSb$_{2}$O$_{9}$

Ba$_{3}$CoSb$_{2}$O$_{9}$ is a spin-1/2 triangular-lattice antiferromagnet with uniform bond length that has attracted a lot of attention in the past decade. This compound is recognized as an ideal material to study the interplay between frustration, low-dimensionality, and strong quantum fluctuations. Both neutron diffraction and inelastic neutron scattering measurements were performed on Ba$_{3}$CoSb$_{2}$O$_{9}$ are obtained by the neutron scattering technique. According to our unpolarized and polarized neutron diffraction measurements, the Co$^{2+}$ magnetic moments form a 120 degree structure in the easy ab-plane. The intra- and inter-plane exchange interactions were determined by fitting the measured spin-wave dispersion with an S$=$1/2 XXZ model.