Wave propagation and group velocity

The plasmon-induced transparency (PIT), which is destructive interference between the superradiation mode and the subradiation mode, is studied in patterned graphene-based terahertz metasurface composed of graphene ribbons and graphene strips. As the results of finite-difference time-domain (FDTD) simulation and coupled-mode theory (CMT) fitting, the PIT can be dynamically modulated by the dual-mode. The left (right) transmission dip is mainly tailored by the gate voltage applied to graphene ribbons (stripes), respectively, meaning a dual-mode on-to-off modulator is realized. Surprisingly, an absorbance of 50% and slow-light property of 0.7 ps are also achieved, demonstrating the proposed PIT metasurface has important applications in absorption and slow-light. In addition, coupling effects between the graphene ribbons and the graphene strips in PIT metasurface with different structural parameters also are studied in detail. Thus, the proposed structure provides a new basis for the dual-mode on-to-off multi-function modulators.

/pdf/dual-mode-on-to-off-modulation-of-plasmon-induced-2pwqomo3p7.pdf

Dual-Mode On-to-Off Modulation of Plasmon-Induced Transparency and Coupling Effect in Patterned Graphene-Based Terahertz Metasurface.

Two-dimensional graphene monolayers and bilayers exhibit fascinating electrical transport behaviors. Using infrared spectroscopy, we find that they also have strong interband transitions and that their optical transitions can be substantially modified through electrical gating, much like electrical transport in field-effect transistors. This gate dependence of interband transitions adds a valuable dimension for optically probing graphene band structure. For a graphene monolayer, it yields directly the linear band dispersion of Dirac fermions, whereas in a bilayer, it reveals a dominating van Hove singularity arising from interlayer coupling. The strong and layer-dependent optical transitions of graphene and the tunability by simple electrical gating hold promise for new applications in infrared optics and optoelectronics.

/pdf/gate-variable-optical-transitions-in-graphene-3q6kb2wuwu.pdf

Gate-Variable Optical Transitions in Graphene

Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-005031.pdf

Black Phosphorus Field-effect Transistors

We propose a novel simple patterned monolayer graphene metamaterial structure based on tunable terahertz plasmon-induced transparency (PIT). Destructive interference in this structure causes pronounced PIT phenomenon, and the PIT response can be dynamically controlled by voltage since the existence of continuous graphene bands in the structural design. The theoretical transmission of this structure is calculated by coupled mode theory (CMT), and the results are highly consistent with the simulation curve. After that, the influence of the graphene mobility on the PIT response and absorption characteristics is researched. It is found that the absorption efficiency of our designed structure can reach up to 50%, meaning the structure is competent to prominent terahertz absorber. Moreover, the slow-light performance of this structure is discussed via analyzing the group refractive index and phase shift. It shows that the structure possesses a broad group refractive index band with ultra-high value, and the value is up to 382. This work will diversify the designs for versatile tunable terahertz devices and micro-nano slow-light devices.

Absorption and slow-light analysis based on tunable plasmon-induced transparency in patterned graphene metamaterial.

Dual plasmon-induced transparency (PIT) and plasmon-induced absorption (PIA) are simultaneously achieved in an integrated metamaterial composed of single layer of graphene. Electric field distribution and coupled mode theory (CMT) are used to demonstrate the physical mechanism of dual PIT and PIA, and the theoretical result of CMT is highly consistent with the finite-difference time-domain (FDTD) method simulation result. Further research shows that both the dual PIT and PIA phenomenon can be effectively modulated by the Fermi level, the carrier mobility of the graphene and the refractive index of the surrounding environment. It is meaningful that the absorption of the dual PIA spectrum can be abruptly increased to 93.5% when the carrier mobility of graphene is 0.8m2/Vs. In addition, the group index can be as high as 328. Thus, our work can pave new way for developing excellent slow-light and light absorption functional devices.

Dynamically tunable dual plasmon-induced transparency and absorption based on a single-layer patterned graphene metamaterial

A novel monolayer graphene structure whose unit cell possesses two rectangular defects is proposed. A very obvious dual plasmon-induced transparency (PIT) effect can be successfully achieved by the destructive interference in the terahertz region. The dual PIT effect can be easily tuned by changing the Fermi energy of the monolayer graphene. Since the graphene of our structure exists in a continuous form, we can simply apply a bias voltage to achieve the tuning performance compared to those structures with discontinuous graphene patterns. We have deduced the expression of the theoretical transmittance and the numerical simulation results are very consistent with the theoretical data. Moreover, we find that this structure has a good slow light property and its group refractive index is as high as 545. Thus, the proposed structure and findings may provide a good guidance for the highly tunable optoelectronic devices and excellent slow light device.

https://iopscience.iop.org/article/10.1088/1361-6463/aae9cc/pdf

Dual plasmon-induced transparency and slow light effect in monolayer graphene structure with rectangular defects

https://iopscience.iop.org/article/10.1088/1361-6463/ab2d1e/pdf

Slow light effect based on tunable plasmon-induced transparency of monolayer black phosphorus

A terahertz metasurface consisting of a graphene ribbon and three graphene strips, which can generate a significant triple plasmon-induced transparency (triple-PIT), is proposed to realize a multifunction switch and optical storage. Numerical simulation triple-PIT which is the result of destructive interference between three bright modes and a dark mode can be fitted by coupled mode theory (CMT). The penta-frequency asynchronous and quatary-frequency synchronous switches can be achieved by modulating the graphene Fermi levels. And the switch performance including modulation depth (83.5% < MD < 93.5%) and insertion loss (0.10 dB < IL < 0.26 dB) is great excellent. In addition, the group index of the triple-PIT can be as high as 935, meaning an excellent optical storage is achieved. Thus, the work provides a new method for designing terahertz multi-function switches and optical storages.

Baihui Zhang

Papers

Absorption and slow-light analysis based on tunable plasmon-induced transparency in patterned graphene metamaterial.

Dynamically tunable dual plasmon-induced transparency and absorption based on a single-layer patterned graphene metamaterial

Dual plasmon-induced transparency and slow light effect in monolayer graphene structure with rectangular defects

Slow light effect based on tunable plasmon-induced transparency of monolayer black phosphorus

Terahertz multifunction switch and optical storage based on triple plasmon-induced transparency on a single-layer patterned graphene metasurface.