Static and Dynamical Properties of the Spin-1/2 Equilateral Triangular-Lattice Antiferromagnet Ba$_3$CoSb$_2$O$_9$

TL;DR

This study uses neutron scattering to analyze the magnetic properties of Ba$_3$CoSb$_2$O$_9$, confirming its status as a near-ideal frustrated quantum magnet and revealing quantum fluctuation effects on magnon dispersion.

Contribution

It provides detailed exchange parameters and demonstrates the impact of quantum fluctuations on magnon behavior in a nearly perfect triangular-lattice antiferromagnet.

Findings

Magnetic moments lie in the ab plane at zero field.

Exchange parameters confirm the model's near-ideal frustration.

Quantum fluctuations cause significant magnon dispersion renormalization.

Abstract

We present single-crystal neutron scattering measurements of the spin-1/2 equilateral triangular lattice antiferromagnet Ba$_3$CoSb$_2$O$_9$. Besides confirming that the Co$^{2+}$ magnetic moments lie in the ab plane for zero magnetic field, we determine all the exchange parameters of the minimal quasi-2D spin Hamiltonian, which confirms that Ba$_3$CoSb$_2$O$_9$ is an almost perfect realization of the paradigmatic model of frustrated quantum magnetism. A comparison with linear and nonlinear spin-wave theory reveals that quantum fluctuations induce a strong downward renormalization of the magnon dispersion.