Ultraviolet and visible plasmonic metamaterials made of topological insulator

We provide the first demonstration of plasmonic metamaterials made of a semiconducting material, Bi 1.5 Sb 0.5 Te 1.8 Se 1.2 (BSTS), which is also known as a topological insulator, working at the UV and visible frequencies where finding a good plasmonic material is extremely challenging. Spectroscopic ellipsometry of the material revealed the existence of negative permittivity in the wavelengths 200 – 670 nm, which is rarely seen at the first absorption edge of semiconductors in nature. The negative permittivity is attributed to the combination of bulk interband transitions and surface contribution of the topologically protected states. Metamaterials fabricated from the BSTS crystal show plasmonic resonances from 350 nm to 550 nm while surface gratings exhibit cathodoluminescence peaks from 230 nm to 1050 nm. This finding of new class of materials with high-frequency plasmonic response could advance plasmonics in view of merging plasmonic functionality with electronics thanks to the nature of the material.