Flatness and boundness of photonic drumhead surface state in a metallic lattice

Abstract

Nodal chain (NC) semi-metals have the degeneracy of interlacing rings in their band structure in momentum space. With the projection of degenerate rings towards crystal boundaries, there is a special type of surface dispersion appearing at surface Brillouin zone and termed drumhead surface state (DSS). Previously, experimental investigations on photonic NC and DSS have been done on metallic photonic crystals at microwave frequencies. However, far-field detection of DSS and its coupling to radiative modes in free space have not been studied. In the work, we analyze the photonic DSS in a metallic lattice by angle-resolved far-field reflection measurement and numerical simulation at terahertz (THz) frequencies, and reveal its flatness and boundness in band structure, even in the radiation continuum. Particularly, the DSS band can be tuned being from negatively dispersive via flat to positively dispersive by a single surface parameter, and the DSS at Γ point in surface Brillouin zone is in fact a symmetry-protected bound state in the continuum. Our results might have some potential applications towards THz photonics.

Nodal lines in momentum space: topological invariants and recent realizations in photonic and other systems

“…Additionally, applications for surface ferromagnetism [186] and high harmonic generation [187] have been theoretically proposed. For photonic applications, high density of states of surface states in nodal lines systems [21,22] are expected to enhance spontaneous emission, resonant scattering, nonlinearities and blackbody radiation. The bound states in the continuum related to nodal lines [31] may find applications in lasing [188] and sensing [189].…”

“…Recently, the drumhead surface states were also shown in phononic crystals [89]. Y. Wang et al analyzed the flatness and boundedness of photonic drumhead surface states using a simple cubic lattice of metals [21].…”

“…By recovering the broken symmetry in a structure with Dirac/Weyl points, i.e., making it P and T symmetric, a nodal line [15][16][17][18], a one-dimensional degeneracy, can be created. Nodal lines have drawn attention because they can feature two-dimensional surface states bounded by the projected nodal lines, called drumhead surface states [19][20][21], and exhibit non-Abelian band topology [17]. Moreover, as nodal lines have higher dimensions than Dirac/Weyl points, they show various shapes, for instance, a simple nodal line, a nodal ring [22][23][24], nodal knots [25][26][27] for a single nodal line or a Hopf link [18,[27][28][29][30][31], a nodal chain [18,[32][33][34] for multiple nodal lines.…”

A brief review of topological photonics in one, two, and three dimensions

“…Apart from a single nodal ring, two or more rings could chain together via touching points forming nodal chains. Nodal chains have been experimentally studied in metallic-mesh photonic crystals [322,323] (see Fig. 11c) and bi-anisotropic metamaterials [324].…”

Towards Perfect Ultra-Broadband Absorbers, Ultra-Narrow Waveguides, and Ultra-Small Cavities at Optical Frequencies

“…The materials have a high carrier concentration and low mobility; this entails a substantially negative real permittivity and material loss [12], which are accountable for reflectance and absorption, respectively. Due to the reflection, a metallic photonic bandgap (PBG), a frequency region that acts as a mirror to block electromagnetic waves, appears in MPHCs [7,[13][14][15]. Several crucial optical components have been designed, such as filters [16,17], waveguides [18,19], and cavities [20,21], using PBGs.…”