Chiral phonons have recently been explored as a novel degree of freedom in quantum materials. The angular momentum carried by these quasiparticles is generated by the breaking of chiral degeneracy of phonons, owing to the chiral lattice structure or the rotational motion of ions of the material. In ferromagnets, a mechanism for generating non-equilibrium chiral phonons has been suggested, but their temporal evolution, which obeys Bose–Einstein statistics, remains unclear. Here we report the real-time dynamics of thermalized chiral phonons in an artificial superlattice composed of ferromagnetic metallic SrRuO₃ and non-magnetic insulating SrTiO₃. Following the photo-induced ultrafast demagnetization in the SrRuO₃ layer, we observed the appearance of a magneto-optic signal in the superlattice, which is absent in the SrRuO₃ single films. This magneto-optic signal exhibits thermally driven dynamic properties and a clear correlation with the thickness of the non-magnetic SrTiO₃ layer, implying that it originates from thermalized chiral phonons. We use numerical calculations considering the magneto-elastic coupling in SrRuO₃ to validate our experimental observations and the angular momentum transfer mechanism between the lattice and spin systems in ferromagnetic systems and also to the non-magnetic system.

手性声子最近被探索为量子材料中的一种新型自由度。由于材料的手性晶格结构或离子的旋转运动，这些准粒子携带的角动量是通过声子手性简并性的破坏而产生的。在铁磁体中，已经提出了一种产生非平衡手性声子的机制，但它们服从玻色-爱因斯坦统计的时间演化仍不清楚。在这里，我们报告了由铁磁金属 SrRuO ₃ 和非磁绝缘 SrTiO ₃ 组成的人造超晶格中热化手性声子的实时动力学。在 SrRuO ₃ 层中发生光致超快退磁后，我们观察到超晶格中出现磁光信号，而 SrRuO ₃ 单层薄膜中不存在这种信号。该磁光信号表现出热驱动的动态特性，并且与非磁性 SrTiO ₃ 层的厚度具有明显的相关性，这意味着它源自热化手性声子。我们使用考虑 SrRuO ₃ 中磁弹性耦合的数值计算来验证我们的实验观察以及铁磁系统和非磁性系统中晶格和自旋系统之间的角动量传递机制。