Spin-phonon coupling (SPC) plays a critical role in numerous intriguing phenomena of transition metal oxides (TMOs). In 3d and 4d TMOs, the coupling between spin and lattice degrees of freedom is known to originate from the exchange interaction. On the other hand, the origin of SPC in 5d TMOs remains to be elucidated. To address this issue, we measured the phonon spectra of the 5d pyrochlore iridate Y₂Ir₂O₇ using optical spectroscopy. Three infrared-active phonons soften below the Néel temperature of T_N ≈ 170 K, indicating the existence of strong SPC. Simulations using density functional theory showed that the coupling is closely related to the Ir–O–Ir bond angle. A tight-binding model analysis reveals that this SPC is mainly mediated by the Dzyaloshinskii–Moriya interaction rather than the usual exchange interaction. We suggest that such unconventional SPC may be realized in other 5d TMOs with non-collinear magnetic order.

自旋声子耦合（SPC）在过渡金属氧化物（TMO）的许多有趣现象中起着至关重要的作用。在3d和4d TMO中，已知自旋和晶格自由度之间的耦合源自交换相互作用。另一方面，尚需阐明SPC在5 d TMO中的起源。为了解决这个问题，我们使用光谱仪测量了5 d烧绿石铱酸盐Y ₂ Ir ₂ O ₇的声子光谱。三个红外活性声子在Néel温度T _N以下软化≈170 K，表明存在强大的SPC。使用密度泛函理论的模拟表明，耦合与Ir–O–Ir键角密切相关。紧密绑定模型分析显示，此SPC主要是由Dzyaloshinskii-Moriya交互作用而不是通常的交换交互作用介导的。我们建议这种非常规的SPC可以在具有非共线磁性顺序的其他5 d TMO中实现。