Strain effect on circularly polarized electroluminescence (EL) is theoretically analyzed for a p-in junction of transition metal dichalcogenides. The electrically controllable circularly polarized EL without the strain effect is understood by valley polarization combined with the electron-hole asymmetry due to the trigonal warping effect in the valence band. The strain enhances circularly polarized EL more efficiently than the trigonal warping effect since the asymmetry occurs in the same direction as the direction of the applied electric field. The calculated result shows that the circular polarization in the strained MoS 2 becomes 100% without losing the EL intensity.

We experimentally demonstrated significant enhancement of terahertz-wave absorption in monolayer graphene by simply sandwiching monolayer graphene between two dielectric media in a total internal reflection geometry. In going through this structure, the evanescent wave of the incident terahertz beam interacts with the sandwiched graphene layer multiple (up to four) times at varying incidence angles. We observed extremely large attenuation (up to ∼ 70% per reflection), especially for s-polarized radiation. The experimental results are quantitatively consistent with our calculations, where we modeled the experiment as an electromagnetic wave reflection process in monolayer graphene. We also derived analytical expressions for the absorptance, showing that the absorptance is proportional to the amount of Joule heating on the graphene surface induced by the terahertz radiation.

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We theoretically investigate intersubband plasmon excitations in doped single wall carbon nanotubes (SWNTs) by examining the dependence of plasmon frequency on the nanotube diameter, chirality, and Fermi energy. The intersubband plasmons can be excited by light with polarization perpendicular to the nanotube axis and thus the plasmon excitations corresponds to optical transitions between the two different subbands, which are sensitive to the Fermi energy. In every SWNT, this mechanism leads to the emergence of the optical absorption peak at the plasmon frequency for a given Fermi energy, EF . The plasmon frequencies calculated for many SWNTs with diameter dt < 2 nm exhibit a dependence on (1/dt) 0.7 and the frequencies are further affected by Fermi energy as E 0.25 F . With this knowledge, it is possible to develop a map of intersubband plasmon excitations in doped SWNTs that could be useful to quickly estimate the doping level and also be an alternative way to characterize nanotube chirality.

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Undoped graphene is known to absorb 2.3% of visible light at a normal angle of incidence. In this paper, we theoretically demonstrate that the absorption of 10–100 GHz of an electromagnetic wave can be tuned from nearly 0 to 100% by varying the Fermi energy of graphene when the angle of incidence of the electromagnetic wave is kept within total internal reflection geometry. We calculate the absorption probability of the electromagnetic wave as a function of the Fermi energy of graphene and the angle of incidence of the wave. These results open up possibilities for the development of simple electromagnetic wave-switching devices operated by gate voltage.

The interband optical conductivity of undoped graphene gives only 2.3% absorption of light regardless of the light frequency. In this work, we show that by enhancing the electric field on a graphene surface through the interference effect, the light absorption of an undoped monolayer graphene can be much enhanced up to 50%. The monolayer graphene is put at the center of a specially designed multilayer structure of dielectric media. The enhanced absorption can be achieved for any arbitrary frequency by changing the number of layers or the refractive index of the layers. We also show that the absorption of light is used by Joule's heating of graphene which can be applied for local heating by light.

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