Surface phonon polaritons (SPhPs) are mixed light-matter states originating from strong coupling of photons with lattice vibrations. Thin films of polar dielectrics feature a splitting of the SPhP branch due to the hybridization of the top and bottom interface modes. Recently, enhanced in-plane thermal conductivity and near-field energy transfer have been experimentally demonstrated in free-standing polar films. These effects are determined by the SPhP dispersion in these systems, which, however, is yet to be reported experimentally. In this work, we retrieve the SPhP dispersion in silicon carbide free-standing membranes few hundreds of nanometers thick through near-field spectroscopy. We find several branches in the experimental dispersion, which we rationalize as multiple reflections of tip and edge launched SPhPs, in good agreement with theoretical predictions. Our work paves the way to employ large-area free-standing membranes as a platform for phonon polaritonics, with foreseeable applications in the field of thermal management at the nanoscale.

中文翻译：

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独立碳化硅薄膜中表面声子极化子色散的近场检索

表面声子极化激元 (SPhPs) 是混合光物质态，源于光子与晶格振动的强耦合。由于顶部和底部界面模式的混合，极性电介质薄膜具有 SPhP 分支的分裂。最近，增强的面内热导率和近场能量转移已经在独立的极性薄膜中进行了实验证明。这些影响是由这些系统中的 SPhP 分散决定的，然而，这尚未通过实验报告。在这项工作中，我们通过近场光谱检索了数百纳米厚的碳化硅独立膜中的 SPhP 分散体。我们在实验分散中发现了几个分支，我们将其合理化为尖端和边缘发射的 SPhP 的多次反射，与理论预测非常吻合。我们的工作为使用大面积独立膜作为声子极化学平台铺平了道路，并在纳米级热管理领域具有可预见的应用。