Department of Physics, University of Regensburg, 93040 Regensburg, Germany.
NEST, CNR - Istituto Nanoscienze and Scuola Normale Superiore, 56127 Pisa, Italy.
Nat Nanotechnol. 2017 Mar;12(3):207-211. doi: 10.1038/nnano.2016.261. Epub 2016 Dec 12.
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 and tailored nanophotonics. Graphene and its heterostructures have attracted particular attention because the absence of an energy gap allows plasmon polaritons to be tuned continuously. Here, we introduce black phosphorus 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 SiO/black phosphorus/SiO heterostructure in which the surface phonon modes of the SiO layers hybridize with surface plasmon modes in black phosphorus that can be activated by photo-induced interband excitation. Within the Reststrahlen band of SiO, 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杂交以形成表面等离激元的可能性使范德瓦尔斯层状材料成为极端光限制和定制纳米光子学的通用平台。由于不存在能隙，石墨烯及其异质结构引起了人们的特别关注，因为等离子体激元可以连续调谐。在这里，我们引入了黑磷作为表面等离激元学中的一种有前途的新材料，它具有超快开关的关键优势。与石墨烯不同，黑磷是一种范德瓦尔斯键合半导体，它允许通过超短近红外脉冲对电子-空穴对进行高对比度的带间激发。在这里，我们设计了一个 SiO/黑磷/SiO 异质结构，其中 SiO 层的表面声子模式与黑磷中的表面等离激元模式杂交，这些模式可以通过光致带间激发来激活。在 SiO 的 Reststrahlen 带中，混合界面极化激元具有表面声子的特性，具有明确定义的频率和动量以及极好的相干性。在光生电子-空穴等离子体的寿命期间，可以通过耦合到散射型扫描近场光学显微镜设置尖端的宽带中红外脉冲来发射相干混合极化激元波。散射辐射使我们能够在时间、能量和空间上跟踪新的混合模式。我们发现，表面模式可以在 ∼50 fs 内激活，并在 5 ps 内消失，因为黑磷中的电子-空穴对复合。这种瞬态模式的出色开关对比度和开关速度、相干性和恒定的波长使其成为超快纳米光子器件的有前途的候选者。
