Chiral surface plasmon polaritons(SPPs)produced by plasmonic nanowires can be used to enhance molecular spectroscopy for biosensing applications.Nevertheless,the switchable stereoselectivity and detection of various analytes are limited by a lack of switchable,chiral SPPs.Using both finite-element method simulations and analytic calculations,we present a graphene-coated chalcogenide(GCC)nanowire that produces mid-infrared,chiral SPPs.The chiral SPPs can be reversibly switched between“on”(transparent)and“off”(opaque)by non-volatile structural state transitions in the dielectric constants of the chalcogenide glass Ge2Sb2Te5.Furthermore,by controlling the Fermi energy of the graphene-coating layer,the nanowire can output either non-chiral or chiral SPPs.A thermal-electric model was built to illustrate the possibility of ultrafast on/off switching of the SPPs at the terminus of the nanowire.Finally,we show that a selective,lateral sorting of sub-10-nm enantiomers can be achieved via the GCC nanowire.Chiral nanoparticles with opposite handedness experience transverse forces that differ in both their sign and magnitude.Our design may pave the way for plasmonic nanowire networks and tunable nanophotonic devices,which require the ultrafast switching of SPPs,and provide a possible approach for a compact,enantiopure synthesis.
Control of chirality using metamaterials plays a critical role in a diverse set of advanced photonics applications,such as polarization control, bio-sensing, and polarization-sensitive imaging devices. However, this poses a major challenge, as it primarily involves the geometrical reconfiguration of metamolecules that cannot be adjusted dynamically. Real-world applications require active tuning of the chirality, which can easily manipulate the magnitude, handedness, and spectral range of chiroptical response. Here, enabled by graphene, we theoretically reveal a tunable/switchable achiral metasurface in the near-infrared region. In the model, the achiral metasurface consists of an array of circular holes embedded through a metal/dielectric/metal trilayer incorporated with the graphene sheet, where holes occupy the sites of a rectangular lattice. Circular conversion dichroism(CCD) originates from the mutual orientation between the achiral metasurface and oblique incident wave.The achiral metasurface possesses dual-band sharp features in the CCD spectra, which are tuned over a broad bandwidth by electrically modulating the graphene's Fermi level. By selecting aluminium as the metal materials,we numerically achieved strong CCD and considerably reduced materials costs with our nanostructures compared with the typically used noble metals such as gold and silver.
