Light-matter interactions in conventional nanophotonic structures typically lack directionality. For example, differently from microwave antenna systems, most optical emitters (e.g., excited atoms/molecules and simple nanoantennas) exhibit quasi-isotropic dipolar radiation patterns with low directivity. Furthermore, surface waves supported by conventional material substrates do not usually have a preferential direction of propagation, and their wavefront tends to spread as it propagates along the surface, unless the surface or the excitation is properly engineered and structured. In this article, we theoretically demonstrate the possibility of realizing unidirectional and diffractionless surface plasmon polariton modes on a nonreciprocal platform, namely, a gyrotropic magnetized plasma. Based on a rigorous Green’s function approach, we provide a comprehensive and systematic analysis of all the available physical mechanisms that may bestow the system with directionality, both in the sense of one-way excitation of surface waves and in the sense of directive diffractionless propagation along the surface. The considered mechanisms include (i) the effect of strong and weak forms of nonreciprocity, (ii) the elliptic-like or hyperbolic-like topology of the modal dispersion surfaces, and (iii) the source polarization state, with the associated possibility of chiral surface-wave excitation governed by angular-momentum matching. We find that three-dimensional gyrotropic plasmonic platforms support a previously unnoticed wave-propagation regime that exhibit several of these physical mechanisms simultaneously, allowing us to theoretically demonstrate unidirectional surface plasmon polariton modes that propagate as a single ultranarrow diffractionless beam. We also assess the impact of dissipation and nonlocal effects. Our theoretical findings may enable a new generation of plasmonic structures and devices with highly directional response.

Hexagonal boron nitride is a large band-gap insulating material which complements the electronic and optical properties of graphene and the transition metal dichalcogenides. However, the intrinsic optical properties of monolayer boron nitride remain largely unex- plored. In particular, the theoretically expected crossover to a direct-gap in the limit of the single monolayer is presently not confirmed experimentally. Here, in contrast to the tech- nique of exfoliating few-layer 2D hexagonal boron nitride, we exploit the scalable approach of high-temperature molecular beam epitaxy to grow high-quality monolayer boron nitride on graphite substrates. We combine deep-ultraviolet photoluminescence and reflectance spectroscopy with atomic force microscopy to reveal the presence of a direct gap of energy 6.1eV in the single atomic layers, thus confirming a crossover to direct gap in the monolayer limit.

Faraday rotation, being a dispersive effect, is commonly considered as the method of choice for nondestructive detection of spin states. Nevertheless Faraday rotation is inevitably accompanied by spin flips induced by Raman scattering, which compromises nondestructive detection. Here, we derive an explicit general relation relating the Faraday rotation and the spin-flip Raman scattering cross sections, from which precise criteria for nondestructive detection are established. It is shown that, even in ideal conditions, nondestructive measurement of a single spin can be achieved only in anisotropic media. Monolayers of transitions metal dichalcogenides are shown to be promising candidates for this purpose.

The light emission properties of color centers emitting in 3.3–4 eV region are investigated for hydrostatic pressures ranging up to 5 GPa at liquid helium temperature. The light emission energy decreases with pressure less sensitively than the bandgap. This behavior at variance from the shift of the bandgap is typical of deep traps. Interestingly, hydrostatic pressure reveals the existence of levels that vary differently under pressure (smaller increase of the emission wavelength compared to the rest of the levels in this energy region or even decrease of it) with pressure. This discovery enriches the physics of the color centers operating in the UV in hBN.

Radiative heat transfer (RHT) between two metallic nanoparticles clusters in both near field and far field areexplored using many-body radiative heat transfer theory implemented with the coupled electric and magneticdipole (CEMD) approach, which effectively takes into account the contribution of magnetic polarization ofmetallic nanoparticles on heat exchange. The effects of magnetic polarization, many-body interaction (MBI),fractal dimension, and relative orientation of the clusters on RHT were analyzed. The results show thatthe contribution of magnetically polarized eddy-current Joule dissipation dominates the RHT between Agnanoparticle clusters. If the electric polarization (EP approach) only is considered, the heat conductance will beunderestimated as compared with the CEMD approach in both near field and far field regime. The effect of MBIon the RHT between Ag nanoparticle clusters is insignificant at room temperature, which is quite different fromthe SiC nanoparticle clusters. For the latter, MBI tends to suppress RHT significantly. The relative orientationhas remarkable effect on radiative heat flux for clusters with lacy structure when the separation distance is in thenear field. While for the separation distance in far field, both the relative orientation and the fractal dimensionhas a weak influence on radiative heat flux. This work will help the understanding of thermal transport in denseparticulate system.

Nanophotonic circuits using group III-nitrides on silicon are still lacking one key component: efficient electrical injection. In this paper we demonstrate an electrical injection scheme using a metal microbridge contact in thin III-nitride on silicon mushroom-type microrings that is compatible with integrated nanophotonic circuits with the goal of achieving electrically injected lasing. Using a central buried n-contact to bypass the insulating buffer layers, we are able to underetch the microring, which is essential for maintaining vertical confinement in a thin disk. We demonstrate direct current room-temperature electroluminescence with 440 mW/cm 2 output power density at 20 mA from such microrings with diameters of 30 to 50 µm. The first steps towards achieving an integrated photonic circuit are demonstrated.