Department of Physics, Columbia University, New York, NY, USA.
Department of Physics, University of California, San Diego, La Jolla, CA, USA.
Nature. 2018 May;557(7706):530-533. doi: 10.1038/s41586-018-0136-9. Epub 2018 May 23.
Plasmon polaritons are hybrid excitations of light and mobile electrons that can confine the energy of long-wavelength radiation at the nanoscale. Plasmon polaritons may enable many enigmatic quantum effects, including lasing , topological protection and dipole-forbidden absorption . A necessary condition for realizing such phenomena is a long plasmonic lifetime, which is notoriously difficult to achieve for highly confined modes . Plasmon polaritons in graphene-hybrids of Dirac quasiparticles and infrared photons-provide a platform for exploring light-matter interaction at the nanoscale. However, plasmonic dissipation in graphene is substantial and its fundamental limits remain undetermined. Here we use nanometre-scale infrared imaging to investigate propagating plasmon polaritons in high-mobility encapsulated graphene at cryogenic temperatures. In this regime, the propagation of plasmon polaritons is primarily restricted by the dielectric losses of the encapsulated layers, with a minor contribution from electron-phonon interactions. At liquid-nitrogen temperatures, the intrinsic plasmonic propagation length can exceed 10 micrometres, or 50 plasmonic wavelengths, thus setting a record for highly confined and tunable polariton modes. Our nanoscale imaging results reveal the physics of plasmonic dissipation and will be instrumental in mitigating such losses in heterostructure engineering applications.
等离子体激元是光和可移动电子的混合激发，可将长波长辐射的能量限制在纳米尺度。等离子体激元可能会实现许多神秘的量子效应，包括激光、拓扑保护和偶极禁吸收。实现这些现象的一个必要条件是长等离子体寿命，对于高度受限的模式，这是众所周知难以实现的。在狄拉克准粒子和红外光子的石墨烯杂化中，等离子体激元为探索纳米尺度的光物质相互作用提供了一个平台。然而，石墨烯中的等离子体耗散很大，其基本限制仍未确定。在这里，我们使用纳米尺度的红外成象技术来研究在低温下封装在高迁移率石墨烯中的传播等离子体激元。在这种情况下，等离子体激元的传播主要受到封装层的介电损耗的限制，电子-声子相互作用的贡献较小。在液氮温度下，本征等离子体传播长度可以超过 10 微米，或 50 个等离子体波长，从而为高度受限和可调谐的极化激元模式创造了记录。我们的纳米尺度成像结果揭示了等离子体耗散的物理机制，并将有助于在异质结构工程应用中减轻这种损耗。
