Ultrahigh Purcell Factor in a Hybrid Plasmonic Crystal Nanobeam Cavity with an Atomically Smooth Single-Crystalline Gold Microflake

We experimentally demonstrated a hybrid plasmonic crystal nanobeam cavity (HPCNC) by transferring an atomically smooth single-crystalline gold microflake (GMF) onto a thermally oxidized silicon photonic crystal nanobeam waveguide with a highly confined cavity mode in a nanoscale low-index layer. The device exhibited an ultrahigh Purcell factor of 3217 at telecommunication wavelengths. This significant enhancement is attributed to the combination of the low-loss single-crystalline plasmonic platform and the deepsubwavelength mode confinement enabled by the hybrid plasmonic waveguide (HPW).