Cherenkov radiation (CR) excited by fast charges can serve as on-chip light sources with a nanoscale footprint and broad frequency range. The reversed CR, which usually occurs in media with the negative refractive index or negative group-velocity dispersion, is highly desired because it can effectively separate the radiated light from fast charges thanks to the obtuse radiation angle. However, reversed CR at the mid-infrared remains challenging due to the significant loss of conventional artificial structures. Here we observe mid-infrared analogue polaritonic reversed CR in a natural van der Waals (vdW) material (i.e., α-MoO₃), whose hyperbolic phonon polaritons exhibit negative group velocity. Further, the real-space image results of analogue polaritonic reversed CR indicate that the radiation distributions and angles are closely related to the in-plane isofrequency contours of α-MoO₃, which can be further tuned in the heterostructures based on α-MoO₃. This work demonstrates that natural vdW heterostructures can be used as a promising platform of reversed CR to design on-chip mid-infrared nano-light sources.

由快速充电激发的切伦科夫辐射 (CR) 可以用作具有纳米级足迹和宽频率范围的片上光源。通常发生在具有负折射率或负群速度色散的介质中的反向 CR 是非常需要的，因为由于钝角的辐射角，它可以有效地将辐射光与快电荷分开。然而，由于传统人工结构的显着损失，中红外的反向 CR 仍然具有挑战性。在这里，我们在天然范德华 (vdW) 材料（即 α-MoO ₃), 其双曲声子极化子表现出负群速度。_{此外，模拟极化反转CR的实空间图像结果表明辐射分布和角度与α-MoO 3}的面内等频轮廓密切相关，可以在基于α-MoO 3 的异质结构中进一步_调整. 这项工作表明，天然 vdW 异质结构可以用作反向 CR 的有前途的平台来设计片上中红外纳米光源。