Optically Unraveling the Edge Chirality‐Dependent Band Structure and Plasmon Damping in Graphene Edges

confinements [5] and substantially low loss, [6] and can be actively controlled via external stimuli. [7][8][9][10] These virtues make the GPs highly attractive for tunable nanophotonics devices. In addition to the sheet plasmon modes which propagate within the 2D plane, there exists another type of plasmon modes, that is, 1D edge plasmon modes propagating along the graphene edge. [11] In comparison to the sheet modes, the edge modes can exhibit enhanced electromagnetic field confinements. [12] Monolayer graphene is terminated by two types of edge with different chiralities, that is, zigzag and armchair edges. [13,14] These two edges give rise to a variety of intriguing localized electronic states that are associated with superconductivity, [15] localized magnetism, [16][17][18] and topological states, [19] among others. Moreover, the physical and chemical properties on the edges are strongly dependent on the termination type. For example, zigzag edge can result in a band of zero-energy modes that is absent in the armchair case. [20] Furthermore, the two edges exhibit different electronic density of states and vacuum potential barriers, making their charge-transfer behaviors and molecule adsorption abilities different from each other. [20,21] These characteristics are anticipated to endow the 1D edge plasmon modes with topology-specific behaviors that are not observed in the sheet modes. [22] Moreover, the evolution of the edge plasmon modes in response to external stimuli, such as electrical gating, chemical doping, and magnetic field, can in turn help reveal the fine electronic structure at these two edges. A few studies have identified that plasmon behaviors associated with these two edges are different because of the edge-specific electronic band structure. However, they only focused on the impact of chirality on the reflections of the sheet plasmons modes at the edges. [22] A direct characterization and comparison of the 1D edge plasmons propagating along the zigzag and armchair edges are still incomplete.Here, we present the study on 1D edge plasmon modes in a monolayer graphene. Using real-space nano-imaging, we for the first time manage to visualize and compare the edge plasmon modes propagating respectively along the zigzag and armchair edges. The results show that in the pristine graphene, the plasmon wavelengths of zigzag and armchair edges are the same and shorter than those of the sheet modes, suggesting a stronger electromagnetic field confinement. Furthermore, upon chemical doping via HNO 3 exposure, the plasmon wavelengths Graphene plasmons (GPs) have a variety of potential applications in nanophotonics and optoelectronics, such as room temperature mid-infrared photodetectors, sensors, and modulators, due to their ultrahigh electromagnetic field confinements. In particular, the GPs at the edges of a monolayer graphene have been demonstrated to exhibit superior electromagnetic field confinements compared to the sheet plasmons. The graphene is terminated by two types of edges with different chiralit...

Section: Resultscontrasting

confidence: 44%

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confidence: 99%

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confidence: 99%

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A Nano‐Imaging Study of Graphene Edge Plasmons with Chirality‐Dependent Dispersions

Wang

Zheng

et al. 2021

“…For pristine GPs, the relationship between wavelength and doping is described by the following scaling law:

λ_{normalp} \propto E_{normalF} \propto \sqrt{n}

which can be derived from a general relationship between 2D plasmons and 2D material conductivity, q p (ω) = [ iω (1 + ε sub (ω))]/4 πσ (ω), and the relationship between graphene conductivity σ and the Fermi level E F ,

σ (ω) = (\frac{i}{π}) [D / (ω + i τ^{- 1})]

, and D = ( e 2 /πℏ 2 ) E F , where D is the Drude weight. Combining them together, we get the famous relationship between a GP wavelength and the carrier density

λ_{normalp} (ω) = \frac{8 π e^{2} v_{normalF} \sqrt{π n}}{ℏ ω^{2} (1 + ϵ_{normalsub} (ω))}

where v F ≈ c /300 ≈ 10 6 m s −1 is the Fermi velocity 16b,22. Equation tells us that

λ_{normalp} \propto \sqrt{n}

, indicating that the wavelength λ p changes sensitively with the carrier concentration n .…”

Section: Scaling Behaviors Of the Polariton Wavelength In Low‐dimensimentioning

confidence: 99%

Scaling and Reflection Behaviors of Polaritons in Low‐Dimensional Materials

Shen

Luo

Lyu

et al. 2019

Polaritons in low‐dimensional materials have shown their unique capabilities to concentrate light at the deep subwavelength scale. They behave quite differently from those in conventional metals. On the one hand, the strongly confined polaritons exhibit a large tunability in wavelength following different scaling behaviors in different systems. On the other hand, they show novel reflection behaviors when they encounter topographic boundaries or electronic discontinuities. Here, recent progress on the scaling and reflection behaviors of strongly confined polaritons in three representative low‐dimensional material systems is reviewed. It is shown that the polariton wavelength changes sensitively with carrier density, thickness, and the number of conducting channels for graphene, hexagonal boron nitride, and carbon nanotubes. Also, it is demonstrated how polaritons reflect in low‐dimensional materials when encountering edges, corrugations, domain walls, strain regions, etc.

“…[ 1–5 ] Graphene as a promising candidate has been intensively researched due to its unusual electro‐optical properties. [ 6–17 ] To date, various methods have been adopted to design the modulator with high efficiency, including large chemical doping, [ 18–20 ] coupling with an additional resonator, [ 21–24 ] and integrating with Salisbury screens (consisting of a single reflective mirror). [ 25–30 ] However, those methods also have some limitations.…”

Section: Introductionmentioning

confidence: 99%

Transmission‐Type Optical Modulator Based on Graphene Plasmonic Resonator Integrated with Off‐Resonant Au Structure

Xia

Wang

Zhang

et al. 2020

In this paper, a transmission‐type graphene plasmonic modulator by introducing off‐resonant Au structure is theoretically and experimentally investigated. It is found that the modulation efficiency and bandwidth could be dramatically enhanced compared with bare graphene plasmonic structure. The validity of this proposed method is verified both in the 1D and 2D graphene plasmonic structures: ribbons and holes. This work will open up a new path to design the high‐efficiency modulators, switches, and multispectral detectors.