The possibility of hybridizing collective electronic motion with mid-infrared light to form surface polaritons has made van der Waals layered materials a versatile platform for extreme light confinement^1,2,3,4,5 and tailored nanophotonics^6,7,8. Graphene^9,10 and its heterostructures^11,12,13,14 have attracted particular attention because the absence of an energy gap allows plasmon polaritons to be tuned continuously. Here, we introduce black phosphorus^{15,16,17,18,19} as a promising new material in surface polaritonics that features key advantages for ultrafast switching. Unlike graphene, black phosphorus is a van der Waals bonded semiconductor, which enables high-contrast interband excitation of electron–hole pairs by ultrashort near-infrared pulses. Here, we design a SiO₂/black phosphorus/SiO₂ heterostructure in which the surface phonon modes of the SiO₂ layers hybridize with surface plasmon modes in black phosphorus that can be activated by photo-induced interband excitation. Within the Reststrahlen band of SiO₂, the hybrid interface polariton assumes surface-phonon-like properties, with a well-defined frequency and momentum and excellent coherence. During the lifetime of the photogenerated electron–hole plasma, coherent hybrid polariton waves can be launched by a broadband mid-infrared pulse coupled to the tip of a scattering-type scanning near-field optical microscopy set-up. The scattered radiation allows us to trace the new hybrid mode in time, energy and space. We find that the surface mode can be activated within ∼50 fs and disappears within 5 ps, as the electron–hole pairs in black phosphorus recombine. The excellent switching contrast and switching speed, the coherence properties and the constant wavelength of this transient mode make it a promising candidate for ultrafast nanophotonic devices.

将集体电子运动与中红外光混合以形成表面极化子的可能性使范德华分层材料成为了一种用于极端光限制^1,2,3,4,5和量身定制的纳米光子学^6,7,8的多功能平台。石墨烯^9,10及其异质结构^11,12,13,14引起了人们的特别关注，因为不存在能隙使等离子体激元极化子连续可调。在这里，我们介绍黑磷^{15,16,17,18,19}作为表面极化电子学中有希望的新材料，它具有超快开关的关键优势。与石墨烯不同，黑磷是范德华键合半导体，可通过超短近红外脉冲对电子-空穴对进行高对比度带内激发。在这里，我们设计了一种SiO ₂ /黑磷/ SiO ₂异质结构，其中SiO ₂层的表面声子模式与黑磷中的表面等离振子模式杂交，可以通过光诱导的带间激发将其激活。在SiO ₂的Reststrahlen带内，混合界面极化子具有类似于表面声子的特性，具有明确的频率和动量以及出色的相干性。在光生电子空穴等离子体的寿命期间，相干混合极化波可以通过与散射型扫描近场光学显微镜装置尖端耦合的宽带中红外脉冲发射。散射的辐射使我们能够在时间，能量和空间上追踪新的混合模式。我们发现，由于黑磷中的电子-空穴对重新结合，表面模式可以在约50 fs内激活，并在5 ps内消失。出色的开关对比度和开关速度，相干特性以及此瞬态模式的恒定波长使其成为超快纳米光子器件的有希望的候选者。