Dynamic tailoring of electromagnetic behaviors of graphene plasmonic oligomers by local chemical potential.

In the mid-infrared and terahertz (THz) regime, graphene supports tunable surface plasmon resonance (SPR) by controlling the chemical potential, which promotes light-matter interaction at the selected wavelength, showing exceptional promise for optoelectronic applications. In this article, we show that the electromagnetic (EM) response of graphene oligomers can be substantially modified by the modification of the local chemical potential, strengthening or reducing the intrinsic plasmonic modes. The effect mechanism is corroborated by a graphene nanocluster composed of 13 nanodisks with D6h symmetry; by transforming to D3h symmetry, the effect mechanism was retained and more available plasmonic resonance modes appeared. The intriguing properties open a new way to design nanodevices made of graphene oligomers with highly efficient photoresponse enhancement and tunable spectral selectivity for highly accurate photodetection.

Topologically protected edge states in graphene plasmonic crystals.

A two-dimensional graphene plasmonic crystal composed of periodically arranged graphene nanodisks is proposed. We show that the band topology effect due to inversion symmetry broken in the proposed plasmonic crystals is obtained by tuning the chemical potential of graphene nanodisks. Utilizing this kind of plasmonic crystal, we constructed N-shaped channels and realized topologically edged transmission within the band gap. Furthermore, topologically protected exterior boundary propagation, which is immune to backscattering, was also achieved by modifying the chemical potential of graphene nanodisks. The proposed graphene plasmonic crystals with ultracompact size are subject only to intrinsic material loss, which may find potential applications in the fields of topological plasmonics and high density nanophotonic integrated systems.

Electromagnetic field coupling characteristics in graphene plasmonic oligomers: from isolated to collective modes.

In this paper, we propose a plasmonic tetramer composed of coupled graphene nanodisks. The transformation from the isolated to the collective modes of the proposed structure is investigated by analysing the whispering-gallery modes and extinction spectra with various inter-nanodisk gap distances. In addition, the effect of introducing a central nanodisk into the tetramer on the extinction spectra is explored, which leads to Fano resonance. Furthermore, the refractive index sensing properties of the proposed graphene plasmonic oligomer have been demonstrated. The proposed nanostructures might pave the road toward the application of graphene plasmonic oligomers in fields such as nanophotonics, and chemical or biochemical sensing.

Surface-plasmon-polariton whispering-gallery mode analysis of the graphene monolayer coated InGaAs nanowire cavity.

In this article, we proposed and numerically studied the surface plasmon polariton whispering gallery mode properties of the graphene coated InGaAs nanowire cavity. The quality factor and the mode area were investigated as a function of the chemical potential, the cavity radius and the wavelength. A high cavity quality factor of 235 is predicted for a 5 nm radius cavity, accompanied by a mode area as small as3.75×10(-5)(λ(0))(2), when the chemical potential is 1.2 eV. The proposed structure offers a potential solution to high density integration of the nanophotonic devices with an ultra-compact footprint.

Investigation of plasmonic whispering-gallery mode characteristics for graphene monolayer coated dielectric nanodisks.

In this Letter, we theoretically studied high-quality (Q) factor plasmonic whispering-gallery modes (WGMs) with ultrasmall mode volumes in graphene monolayer coated semiconductor nanodisks in the mid-infrared range. The influence of the chemical potential, the relaxation time of graphene, and the radius of the nanodisk on the cavity Q factor and the mode volume was numerically investigated. The numerical simulations showed that the plasmonic WGMs excited in this cavity had a deep subwavelength mode volume of 1.4×10(-5)(λ(0)/2n)(3), a cavity Q factor as high as 266 at a temperature lower than 250 K, and, consequently, a large Purcell factor of ∼1.2×10(7) when the chemical potential and relaxation time were assumed to be 0.9 eV and 1.4 ps, respectively. The results provide a possible application of plasmonic WGMs in the integration of nano-optoelectronic devices based on graphene.

Targeting mesenchymal stem cell therapy for severe pneumonia patients.

Pneumonia is the inflammation of the lungs and it is the world's leading cause of death for children under 5 years of age. The latest coronavirus disease 2019 (COVID-19) virus is a prominent culprit to severe pneumonia. With the pandemic running rampant for the past year, more than 1590000 deaths has occurred worldwide up to December 2020 and are substantially attributable to severe pneumonia and induced cytokine storm. Effective therapeutic approaches in addition to the vaccines and drugs under development are hence greatly sought after. Therapies harnessing stem cells and their derivatives have been established by basic research for their versatile capacity to specifically inhibit inflammation due to pneumonia and prevent alveolar/pulmonary fibrosis while enhancing antibacterial/antiviral immunity, thus significantly alleviating the severe clinical conditions of pneumonia. In recent clinical trials, mesenchymal stem cells have shown effectiveness in reducing COVID-19-associated pneumonia morbidity and mortality; positioning these cells as worthy candidates for combating one of the greatest challenges of our time and shedding light on their prospects as a next-generation therapy to counter future challenges.

Bufalin-induced cardiotoxicity: new findings into mechanisms.

Bufalin is one of the main pharmacological and toxicological components of Venenum Bufonis and many traditional Chinese medicine preparations. The cardiotoxicity clearly limits its application to patients living in countries. Hence, an investigation of its toxicological mechanism is helpful for new drug development and treatment of the related clinical adverse reactions. We investigate the cardiotoxicity of bufalin using human induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs) (0.003-0.1 µmol·L-1), human induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs) (0.03-0.3 µmol·L-1) and eight human cardiac ion channel currents (0.01-100 µmol·L-1) combined with an impedance-based bioanalytical and patch clamp method. Biphasic effect of bufalin on the contractility in hiPSC-CMs, which has been shown to strengthen myocardial contractility, accelerate conduction, and increase beating rate at the earlier stage of administration, whereas weakened myocardial contractility, abolished conduction, and ceased beating rate at the later stage of administration. Bufalin decreased the action potential duration (Action potential duration at 30%, 50% and 90% repolarization), cardiac action potential amplitude, and maximal depolarization rate and depolarized the resting membrane potential of hiPSC-CMs. Spontaneous beating rates of hiPSC-CMs were markedly increased at 0.03 µmol·L-1, while were weakened at 0.3 µmol·L-1 after application. Bufalin blocks INav1.5 in a concentration-dependent manner with half maximal inhibitory concentration of 74.5 µmol·L-1. Bufalin respectively increased the late sodium current and Na+-Ca2+ exchange current with a concentration for 50% of maximal effect of 2.48 and 66.06 µmol·L-1 in hiPSC-CMs. Whereas, bufalin showed no significant effects on other cardiac ion channel currents. The enhancement of the late sodium current is one of the main mechanism for cardiotoxicity of bufalin.

Pseudospin Dependent One-Way Transmission in Graphene-Based Topological Plasmonic Crystals.

Originating from the investigation of condensed matter states, the concept of quantum Hall effect and quantum spin Hall effect (QSHE) has recently been expanded to other field of physics and engineering, e.g., photonics and phononics, giving rise to strikingly unconventional edge modes immune to scattering. Here, we present the plasmonic analog of QSHE in graphene plasmonic crystal (GPC) in mid-infrared frequencies. The band inversion occurs when deforming the honeycomb lattice GPCs, which further leads to the topological band gaps and pseudospin features of the edge states. By overlapping the band gaps with different topologies, we numerically simulated the pseudospin-dependent one-way propagation of edge states. The designed GPC may find potential applications in the fields of topological plasmonics and trigger the exploration of the technique of the pseudospin multiplexing in high-density nanophotonic integrated circuits.

Investigation of beam splitter in a zero-refractive-index photonic crystal at the frequency of Dirac-like point.

The Dirac-like cone dispersion of the photonic crystal induced by the three-fold accidental degeneracy at the Brillouin center is calculated in this paper. Such photonic crystals can be mapped to zero-refractive-index materials at the vicinity of the Dirac-like point frequency, and utilized to construct beam splitter of high transmission efficiency. The splitting ratio is studied as a function of the position of the input/output waveguides. Furthermore, variant beam splitters with asymmetric structures, bulk defects, and some certain bending angles are numerically simulated. Finally, we show that 1 × 2 to 1 × N beam splitting can be realized with high transmission efficiency in such a zero-refractive-index photonic crystal at the frequency of Dirac-like point. The proposed structure could be a fundamental component of the high density photonic integrated circuit technique.

Dynamically Tunable Plasmon-Induced Transparency in On-chip Graphene-Based Asymmetrical Nanocavity-Coupled Waveguide System.

A graphene-based on-chip plasmonic nanostructure composed of a plasmonic bus waveguide side-coupled with a U-shaped and a rectangular nanocavities has been proposed and modeled by using the finite element method in this paper. The dynamic tunability of the plasmon-induced transparency (PIT) windows has been investigated. The results reveal that the PIT effects can be tuned via modifying the chemical potential of the nanocavities and plasmonic bus waveguide or by varying the geometrical parameters including the location and width of the rectangular nanocavity. Further, the proposed plasmonic nanostructure can be used as a plasmonic refractive index sensor with a sensing sensibility of 333.3 nm/refractive index unit (RIU) at the the PIT transmission peak. Slow light effect is also realized in the PIT system. The proposed nanostructure may pave a new way towards the realization of graphene-based on-chip integrated nanophotonic devices.

Optimization of the Fano Resonance Lineshape Based on Graphene Plasmonic Hexamer in Mid-Infrared Frequencies.

In this article, the lineshape of Fano-like resonance of graphene plasmonic oligomers is investigated as a function of the parameters of the nanostructures, such as disk size, chemical potential and electron momentum relaxation time in mid-infrared frequencies. Also, the mechanism of the optimization is discussed. Furthermore, the environmental index sensing effect of the proposed structure is revealed, and a figure of merit of 25.58 is achieved with the optimized graphene oligomer. The proposed nanostructure could find applications in the fields of chemical or biochemical sensing.

Investigation of the Band Structure of Graphene-Based Plasmonic Photonic Crystals.

In this paper, one-dimensional (1D) and two-dimensional (2D) graphene-based plasmonic photonic crystals (PhCs) are proposed. The band structures and density of states (DOS) have been numerically investigated. Photonic band gaps (PBGs) are found in both 1D and 2D PhCs. Meanwhile, graphene-based plasmonic PhC nanocavity with resonant frequency around 175 THz, is realized by introducing point defect, where the chemical potential is from 0.085 to 0.25 eV, in a 2D PhC. Also, the bending wvaguide and the beam splitter are realized by introducing the line defect into the 2D PhC.

Structural, electronic and magnetic effects of Al-doped niobium clusters: a density functional theory study.

The application of the ab initio stochastic search procedure with Saunders "kick" method has been carried out for the elucidation of global minimum structures of a series of Al-doped clusters, Nb(n)Al (1 ≤ n ≤ 10). We have studied the structural characters, growth behaviors, electronic and magnetic properties of Nb(n)Al by the density functional theory calculations. Unlike the previous literature reported on Al-doped systems where ground state structures undergo a structural transition from the Al-capped frame to Al-encapsulated structure, we found that Al atom always occupies the surface of Nb(n)Al clusters and structural transition does not take place until n = 10. Note that the fragmentation proceeds preferably by the ejection of an aluminum atom other than niobium atom. According to the natural population analysis, charges always transfer from aluminum to niobium atoms. Furthermore, the magnetic moments of the Nb(n)Al clusters are mainly located on the 4d orbital of niobium atoms, and aluminum atom possesses very small magnetic moments.

Mode coupling between first- and second-order whispering-gallery modes in coupled microdisks.

The mode characteristics for two coupled microdisks are investigated by the finite-difference time-domain technique. In the two coupled micodisks, mode coupling between the same order whispering-gallery modes (WGMs) results in coupled WGMs with split mode wavelengths. The numerical results show that the split mode wavelengths of the coupled first- and second-order WGMs can have a crossing point in some cases, which can induce anticrossing mode coupling between them and greatly reduce the mode Q factor of the coupled first-order WGMs. The time variation of mode field pattern shows the transformation between the coupled first- and second-order WGMs.