Magnon-induced scalar spin chirality in kagome and honeycomb ferromagnets

Abstract

The scalar spin chirality (SSC), defined as a triple product of spins, is essential for describing noncoplanar spin structures and understanding chiral physics in magnetic systems. Traditionally, SSC has been discussed primarily in the context of noncoplanar ground-state spin configurations at zero temperature, as collinear spin systems are generally thought to lack SSC. Consequently, whether the SSC can emerge at finite temperatures in spin systems with collinear ground states remains an open question and has yet to be fully understood. In this study, we theoretically demonstrate that thermally excited magnons can induce SSC even in collinear spin systems. By considering two-dimensional ferromagnets on kagome and honeycomb lattices, we demonstrate that the Dzyaloshinskii-Moriya interactions (DMI), which break effective time-reversal symmetry of the system, lead to the emergence of finite SSC fluctuations at finite temperatures. Using a simple spin model, we show both numerically and analytically that the SSC increases with the magnitude of DMI and temperature. Furthermore, calculations based on realistic material parameters reveal that the magnon-induced SSC can achieve a magnitude comparable to those observed in noncoplanar spin configurations. These findings suggest that SSC plays a significant role even in collinear spin systems, providing insights into the chiral physics of magnetic materials.