Eini Tomer, Quintela M F C Martins, Henriques J C G, Ribeiro R M, Mazor Yarden, Peres N M R, Epstein Itai
Tel Aviv University, School of Electrical Engineering, Faculty of Engineering, Tel Aviv 6997801, Israel.
Department of Physics and Physics Center of Minho and Porto Universities (CF-UM-UP), Campus of Gualtar, 4710-057 Braga, Portugal.
Phys Rev Lett. 2025 May 16;134(19):196903. doi: 10.1103/PhysRevLett.134.196903.
Collective excitations of charged particles under the influence of an electromagnetic field give rise to a rich variety of hybrid light-matter quasiparticles with unique properties. In metals, intraband collective response manifested by negative permittivity leads to plasmon polaritons with extreme field confinement, wavelength "squeezing," and potentially low propagation losses. In contrast, photons in semiconductors commonly couple to interband collective response in the form of exciton polaritons, which give rise to completely different polaritonic properties, described by a superposition of the photon and exciton and an anti-crossing of the eigenstates. In this work, we identify the existence of plasmon-like collective excitations originating from the interband excitonic response of biased bilayer and trilayer graphene, in the form of graphene exciton polaritons (GEPs). We find that GEPs possess electrically tunable polaritonic properties and discover that such excitations follow a universal dispersion law for all surface polaritons in 2D excitonic systems. Accounting for nonlocal corrections to the excitonic response, we find that the GEPs exhibit confinement factors that can exceed those of graphene plasmons, and with moderate losses that would enable their observation in cryo-SNOM experiments. These predictions of plasmon-like interband collective excitations in biased graphene systems open up new research avenues for tunable plasmonic phenomena based on excitonic systems, and the ability to control and manipulate such phenomena at the atomic scale.
在电磁场的影响下，带电粒子的集体激发会产生各种具有独特性质的混合光物质准粒子。在金属中，由负介电常数表现出的带内集体响应会导致具有极端场限制、波长“压缩”以及潜在低传播损耗的等离子体激元极化激元。相比之下，半导体中的光子通常以激子极化激元的形式与带间集体响应耦合，这会产生完全不同的极化激元性质，由光子和激子的叠加以及本征态的反交叉来描述。在这项工作中，我们确定了源自偏置双层和三层石墨烯带间激子响应的类等离子体集体激发的存在，其形式为石墨烯激子极化激元（GEP）。我们发现GEP具有电可调的极化激元性质，并发现这种激发遵循二维激子系统中所有表面极化激元的通用色散定律。考虑到对激子响应的非局部修正，我们发现GEP表现出的限制因子可以超过石墨烯等离子体激元的限制因子，并且具有适度的损耗，这将使其能够在低温扫描近场光学显微镜（cryo-SNOM）实验中被观测到。这些关于偏置石墨烯系统中类等离子体带间集体激发的预测为基于激子系统的可调谐等离子体现象以及在原子尺度上控制和操纵此类现象的能力开辟了新的研究途径。
