Observation of Topological Z₂-vortex Fluctuations in the Frustrated Heisenberg Magnet NaCrO₂

Abstract

Spin fluctuations in the triangular-lattice Heisenberg antiferromagnet NaCrO₂ are investigated by means of quasi-elastic neutron scattering with high energy resolution and a wide energy band. Two components with the following features are captured separately. They are pronounced at intermediate temperatures of 20 to 50 K. One, with quite an extended lifetime corresponding to ∼0.001E_ex (E_ex is the exchange energy), nearly disappears at low temperature (10 K), and the other, with an extended lifetime of ∼0.01E_ex, survives there, identified as the free Z₂ vortex and Z₂-vortex pair, respectively, in agreement with the Z₂-vortex theory. [This article briefly introduces the published paper, K. Tomiyasu et al., Phys. Rev. B 106, 054407 (2022). Please see it for details.]