Fast Switching "On/Off" Chiral Surface Plasmon Polaritons in Graphene-Coated Ge2Sb2Te5 Nanowire

Plasmonic nanowire was found to generate chiral surface plasmon polaritons (SPPs), with the perspective of enhancing molecular spectroscopy for biosensing applications. However, the lack of chiroptical switches exhibits significant limitations in detecting a multitude of various analytes with a high sensitivity and in asymmetric catalysis to provide a switchable stereoselectivity. Here, we numerically and analytically propose a graphene-coated Ge2Sb2Te5 (GST225) nanowire to solve this problem. We highlight that the chiral SPPs propagating along the nanowire can be reversibly switched between "on" (transparent) and "off' (opaque) as transiting the state of GST22S core between amorphous and crystalline. Moreover by changing the Fermi energy of the graphene coating layer, the hybrid nanowire can produce either achiral or chiral SPPs at the output of nanowire. A thermal-electric model is put forward to study the temporal variation of the temperature of the GST225 core. Transiting the structural phase of GST22S in nanosecond was theoretically demonstrated. Our proof of concept permits the preparation of circularly polarized light source with a fast switching "on/off' function. We foresee its potential applications for tunable nanophotonic devices, plasmonic nanowire networks, on-chip biosensing, etc., where the active controlling of SPPs is necessary.