In this paper, a bulk Dirac semimetals (BDSs) based tunable narrowband absorber at terahertz frequencies is proposed and it has the attractive property of being polarization-independent at normal incidence because of its 90° rotational symmetry. Numerical results show that the absorption bandwidth is about 1.469e-2 THz and the total quality factor Q, defined as Q = f/Δf, reaches about 94.6, which can be attributed to the low power loss of the guided mode resonance in the dielectric layer. The simulation results are analyzed with coupled mode theory. Interestingly, on the premise of maintaining the absorbance at a level greater than 0.95, the absorption frequency can be tuned from 1.381 to 1.395 THz by varying the Fermi energy of BDSs from 50 to 80 meV. Our results may also provide potential applications in optical filter and bio-chemical sensing.
General plasmonic systems to realize plasmonically induced transparency (PIT) effect only exist one single PIT mainly because they only allow one single coupling pathway. In this study, we propose a distinct graphene resonator-based system, which is composed of graphene nanoribbons (GNRs) coupled with dielectric gratingloaded graphene layer resonators, to achieve two switchable PIT effects. By designing crossed directions of the resonators, the proposed system exists two different PIT effects characterized by different resonant positions and linewidths. These two PIT effects result from two separate and polarization-selective coupling pathways, allowing us to switch the PIT from one to the other by simply changing the polarization direction. Parametric studies are carried to demonstrate the coupling effects whereas the two-particle model is applied to explain the physical mechanism, finding excellent agreements between the numerical and theoretical results. Our proposal can be used to design switchable PIT-based plasmonic devices, such as tunable dual-band sensors and perfect absorbers.
Using large-scale ab initio calculations and taking the two-dimensional C 2 N monolayer as a substrate, we sampled a large combinatorial space of C 2 N-supported homonuclear and heteronuclear dual-atom catalysts and built a detailed view of catalytic activity and stability toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The results indicate that regulating combinations of metal pairs could widely tune the catalytic performance. Pd 2 −, Pt 2 −, and PdPt−C 2 N could effectively balance the adsorption strength of intermediates and achieve optimal bifunctional activity. The favorable catalytic performance could also be realized on GaPd−C 2 N for the ORR and PdRh−C 2 N for the OER, surpassing corresponding homonuclear counterparts. The thermodynamic and electrochemical stability simulations reveal that these metal pairs can be stably anchored onto the C 2 N matrix. Multiple-level descriptors, including Gibbs free energy, d-band center, and bonding/antibonding orbital population, are established to track the activity trend and reveal the origin of activity, indicating that catalytic activity is intrinsically governed by the d-band center of metal pairs.
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