The origin of phonon thermal Hall Effect (THE) observed in a variety of insulators is yet to be identified. Here, we report on the observation of a thermal Hall conductivity in a non-magnetic elemental insulator, with an amplitude exceeding what has been previously observed. In black phosphorus (BP), the longitudinal (κ_ii), and the transverse, κ_ij, thermal conductivities peak at the same temperature and at this peak temperature, the κ_ij/κ_jj/B is ≈ 10⁻⁴−10⁻³ T⁻¹. Both these features are shared by other insulators displaying THE, despite an absolute amplitude spreading over three orders of magnitude. The absence of correlation between the thermal Hall angle and the phonon mean-free-path imposes a severe constraint for theoretical scenarios of THE. We show that in BP a longitudinal and a transverse acoustic phonon mode anti-cross, facilitating wave-like transport across modes. The anisotropic charge distribution surrounding atomic bonds can pave the way for coupling between phonons and the magnetic field.

在各种绝缘体中观察到的声子热霍尔效应 (THE) 的起源尚未确定。在这里，我们报告了对非磁性元素绝缘体中霍尔热传导率的观察，其幅度超过了之前观察到的幅度。在黑磷 (BP) 中，纵向 ( κ ) 和横向κ热导率在相同温度下达到峰值，并且在此峰值温度下， κ / κ / B为 ≈ 10 ^-4 -10 ^-3 T ^-1 。尽管绝对振幅分布超过三个数量级，但显示 THE 的其他绝缘体也具有这两个特征。热霍尔角和声子平均自由程之间缺乏相关性，对THE的理论场景造成了严格的限制。我们表明，在 BP 中，纵向和横向声子模式反交叉，促进跨模式的波状传输。原子键周围的各向异性电荷分布可以为声子和磁场之间的耦合铺平道路。