Phonon polaritons—light coupled to lattice vibrations—in polar van der Waals crystals are promising candidates for controlling the flow of energy on the nanoscale due to their strong field confinement, anisotropic propagation and ultra-long lifetime in the picosecond range^1,2,3,4,5. However, the lack of tunability of their narrow and material-specific spectral range—the Reststrahlen band—severely limits their technological implementation. Here, we demonstrate that intercalation of Na atoms in the van der Waals semiconductor α-V₂O₅ enables a broad spectral shift of Reststrahlen bands, and that the phonon polaritons excited show ultra-low losses (lifetime of 4 ± 1 ps), similar to phonon polaritons in a non-intercalated crystal (lifetime of 6 ± 1 ps). We expect our intercalation method to be applicable to other van der Waals crystals, opening the door for the use of phonon polaritons in broad spectral bands in the mid-infrared domain.

极性范德华晶体中的声子极化子（与晶格振动耦合的光）因其强大的场限制，各向异性传播和皮秒范围^1,2,3的超长寿命而成为控制纳米级能量流的有希望的候选者^，4,5。但是，它们狭窄的和特定于材料的光谱范围（Reststrahlen波段）缺乏可调性，严重限制了它们的技术实施。这里，我们证明的Na原子的那嵌入在范德华半导体α-V ₂ ø ₅可以实现Reststrahlen谱带的宽谱位移，并且激发的声子极化子显示出超低损耗（寿命为4±1 ps），类似于非插入晶体中的声子极化子（寿命为6±1 ps）。我们希望我们的嵌入方法适用于其他范德华晶体，这为在中红外域的宽光谱带中使用声子极化子打开了大门。