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

The authors combine films of two-dimensional semiconductors, which exhibit excitonic spectral features, with SiO2/Si Fabry-Perot resonators in order to realize topological phase singularities in reflection. Around these singularities, the reflection spectra demonstrate rapid phase changes while the structure behaves as a perfect absorber. 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.

Automated summary

The authors combine films of two-dimensional semiconductors with Fabry-Perot resonators to realize topological phase singularities, expanding the potential of 2D materials in optical applications.