Edge diffraction, plasmon launching, and universal absorption enhancement in two-dimensional junctions
E. I. Nikulin, Dmitry Mylnikov, D. A. Bandurin, Dmitry Svintsov
Abstract
Exact solutions to diffraction problems in wave optics are scarce though strongly demanded for accurate knowledge of electromagnetic fields in the immediate vicinity of scatterers. Here, we obtain and analyze an exact analytical solution for plane-wave diffraction at a lateral junction of two-dimensional (2D) conductors with dissimilar surface conductivities. We find that the junction near fields possesses a dipolelike radiative component and 2D surface-plasmon polaritons launched by the edge. We show that a junction between a perfect metal and an ohmic 2D conductor enhances the local absorbance, which is the ratio of absorbed power density and light intensity. It reaches a universal value of 200% near the 2D edge at normal incidence, independent of absorbance in the bulk. A junction between metal and a 2D conductor also acts as an efficient coupler between photons and 2D plasmons. Its amplitude conversion efficiency demonstrates an unbounded growth with increase in 2D impedance. Our results set the fundamental limits for field enhancement by edges and should change the strategies for design of subwavelength radiation detectors.