Topological phase singularities in atomically thin high-refractive-index materials

Abstract

Atomically thin transition metal dichalcogenides (TMDCs) present a promising platform for numerous photonic applications due to excitonic spectral features, possibility to tune their constants by external gating, doping, or light, and mechanical stability. Utilization of such materials for sensing or optical modulation purposes would require a clever optical design, as by itself the 2D materials can offer only a small optical phase delay – consequence of the atomic thickness. To address this issue, we combine films of 2D semiconductors which exhibit excitonic lines with the Fabry-Perot resonators of the standard commercial SiO2/Si substrate, in order to realize topological phase singularities in reflection. Around these singularities, reflection spectra demonstrate rapid phase changes while the structure behaves as a perfect absorber. Furthermore, we demonstrate that such topological phase singularities are ubiquitous for the entire class of atomically thin TMDCs and other high-refractive-index materials, making it a powerful tool for phase engineering in flat optics. As a practical demonstration, we employ PdSe2 topological phase singularities for a refractive index sensor and demonstrate its superior phase sensitivity compared to typical surface plasmon resonance sensors.

Nonlinear Exciton‐Mie Coupling in Transition Metal Dichalcogenide Nanoresonators

“…Owing to the enormous potential in post‐silicon on‐chip technology, [ 1,2 ] bulk transition metal dichalcogenides (TMDCs) have emerged from the shadows of monolayer counterparts in recent years. Ultrafast photodetection, [ 3,4 ] exciton‐polariton transport, [ 1,5,6 ] strong coupling, [ 7,8 ] Zenneck surface waves, [ 9 ] tunable birefringence, [ 10 ] anapole modes, [ 11,12 ] and ultrasensitive sensors [ 13,14 ] are some of the most well‐known examples. Superior bulk TMDC characteristics, such as high refractive index, [ 15 ] excitonic light–matter interaction, [ 16 ] and giant optical anisotropy, [ 1 ] lie at the core of these advancements.…”

Asymmetric phase modulation of light with parity-symmetry broken metasurfaces

“…[27,[65][66][67]. Our work unifies, via the analysis of complex frequency position of reflection singularities, the physics of the overwhelming majority of MIM phase-gradient metasurfaces operating in reflection [6,7,57,58,[60][61][62][63]. We also rely on a temporal coupled-mode theory to study the positions of the complex topological singularities and to generalize the previously defined overcoupling regime associated with the full-phase modulation regime.…”