Multifunctional graphene metamaterials based on polarization-insensitive plasmon-induced transparency.

In this paper, a 4L-shaped graphene patterned polarization-insensitive plasmon-induced transparency (PIT) metamaterial structure is proposed. The photoelectric switch based on this structure supports a variety of light sources, such as linearly polarized light with different polarization directions, left rotation circularly polarized light (LCP) and right rotation circularly polarized light (RCP). And the switch has excellent performance in the case of different light sources, the amplitude modulation is as high as 99.01%, and the insertion loss is as low as 0.04 dB. In addition, the PIT metamaterial has a high refractive index sensitivity of up to 49156 nm/RIU. The group index of the PIT metamaterial is as high as 980, which can achieve excellent slow light effect. This study provides a scheme and guidance for the design of optoelectronic devices.

Innovative design to achieve a multi-band electromagnetic wave stealth.

Metamaterials have opened up a new field of electromagnetic wave stealth that can achieve cross-band electromagnetic wave stealth through high electromagnetic wave absorption and low infrared emission. However, traditional cross-band stealth metamaterials make covering the terahertz band challenging and have certain design flaws. This Letter introduces an innovative cross-band electromagnetic wave stealth metasurface design that can achieve cross-band stealth in the infrared, microwave, and THz bands. We use phase change materials and the gradient principle to achieve GHz and THz cross-band absorption. We also design surface height-covered low infrared emitting materials, which give them lower infrared emissivity. These functions give it enormous potential in military applications, and using phase change materials for cross-band absorption also provides new, to our knowledge, ideas for multifunctional stealth materials.

Perfect light trapping in nanoscale thickness semiconductor films with a resonant back reflector and spectrum-splitting structures.

The optical absorption of nanoscale thickness semiconductor films on top of light-trapping structures based on optical interference effects combined with spectrum-splitting structures is theoretically investigated. Nearly perfect absorption over a broad spectrum range can be achieved in <100 nm thick films on top of a one-dimensional photonic crystal or metal films. This phenomenon can be attributed to interference induced photonic localization, which enhances the absorption and reduces the reflection of the films. Perfect solar absorption and low carrier thermalization loss can be achieved when the light-trapping structures with a wedge-shaped spacer layer or semiconductor films are combined with spectrum-splitting structures.

Tunable THz absorption in graphene-based heterostructures.

We investigate THz absorption properties of graphene-based heterostructures by using characteristics matrix method based on conductivity. We demonstrate that the proposed structure can lead to perfect THz absorption because of strong photon localization in the defect layer of the heterostructure. The THz absorption may be tuned continuously from 0 to 100% by controlling the chemical potential through a gate voltage. By adjusting the incident angle or the period number of the two PCs with respect to the graphene layer, one can tailor the maximum THz absorption value. The position of the THz absorption peaks can be tuned by changing either the center wavelength or the thicknesses ratio of the layers constituting the heterostructure. Our proposal may have potentially important applications in optoelectronic devices.

Proposal for the momentum-resolved and time-resolved optical measurement of the current distribution in semiconductors.

The two-color optical coherence absorption spectrum (QUIC-AB) of semiconductors in the presence of a charge current is investigated. We find that the QUIC-AB depends strongly not only on the amplitude of the electron current but also on the direction of the electron current. Thus, the amplitude and the angular distribution of current in semiconductors can be detected directly in real time with the QUIC-AB.

N-(2-Chloro-pyrimidin-4-yl)-2-methyl-2H-indazol-6-amine methanol monosolvate.

In the title compound, C(12)H(10)ClN(5)·CH(3)OH, the indazole ring system and the pyrimidine ring make a dihedral angle of 23.86 (4)°. In the crystal, the components are linked by N-H⋯O and O-H⋯N hydrogen bonds into chains propagated in [010]. Inter-molecular π-π inter-actions [centroid-centroid distances = 3.6404 (9), 3.6725 (9) and 3.4566 (9) Å] between the rings of neighbouring chains also stabilize the crystal packing.

Broadband perfect light trapping in the thinnest monolayer graphene-MoS2 photovoltaic cell: the new application of spectrum-splitting structure.

The light absorption of a monolayer graphene-molybdenum disulfide photovoltaic (GM-PV) cell in a wedge-shaped microcavity with a spectrum-splitting structure is investigated theoretically. The GM-PV cell, which is three times thinner than the traditional photovoltaic cell, exhibits up to 98% light absorptance in a wide wavelength range. This rate exceeds the fundamental limit of nanophotonic light trapping in solar cells. The effects of defect layer thickness, GM-PV cell position in the microcavity, incident angle, and lens aberration on the light absorptance of the GM-PV cell are explored. Despite these effects, the GM-PV cell can still achieve at least 90% light absorptance with the current technology. Our proposal provides different methods to design light-trapping structures and apply spectrum-splitting systems.

Omnidirectional bandgaps in Fibonacci quasicrystals containing single-negative materials.

The band structure and bandgaps of one-dimensional Fibonacci quasicrystals composed of epsilon-negative materials and mu-negative materials are studied. We show that an omnidirectional bandgap (OBG) exists in the Fibonacci structure. In contrast to the Bragg gaps, such an OBG is insensitive to the incident angle and the polarization of light, and the width and location of the OBG cease to change with increasing Fibonacci order, but vary with the thickness ratio of both components, and the OBG closes when the thickness ratio is equal to the golden ratio. Moreover, the general formulations of the higher and lower band edges of the OBG are obtained by the effective medium theory. These results could lead to further applications of Fibonacci structures.