Seminar : Spin current as a probe of KT-type topological transitions in magnets
Dr. Kazushi Aoyama - Osaka University, Japan
Spin current as a probe of KT-type topological transitions in magnets
In XY magnets in two dimensions, the Kosterlitz-Thouless(KT) transition, a binding-unbinding topological transition of vortices, occurs. For isotropic Heisenberg spin systems, a similar KT-type transition is also possible in two-dimensional frustrated magnets possessing non-collinear spin correlations. In the triangular-lattice classical Heisenberg antiferromagnet with the nearest-neighbor interaction, the short-range spin correlation of the non-collinear 120° structure yields the so-called Z2 vortex, and the existence of a KT-type topological transition of the Z2 vortices is predicted . In this work, we examine the association between the topological transitions and transport properties of the system.
We will demonstrate by means of the hybrid Monte-Carlo and spin-dynamics simulations that the longitudinal spin-current conductivity exhibits a divergence at the topological transition, while the thermal conductivity does not . The result suggests that the spin-current measurement is a promising probe to detect the KT-type topological transition. In the presentation, we will also discuss the role of the vortex which is topologically stable and thus, has a long lifetime.
 H. Kawamura and S. Miyashita, J. Phys. Soc. Jpn. 53, 4138 (1984).
 K. Aoyama and H. Kawamura, Phys. Rev. Lett. 124, 047202 (2020); Phys. Rev. B 100, 144416 (2019).