PT Symmetry and Singularity-Enhanced Sensing Based on Photoexcited Graphene Metasurfaces

One of graphene's interesting properties is that, when pumped by a laser at near-infrared and visible frequencies, it offers amplification at terahertz (THz) frequencies, which are useful for remote sensing in security applications. The authors explain how to take advantage of exotic parity-time ($P\phantom{\rule{0}{0ex}}T$) symmetry in an active graphene metasurface that realizes reciprocal, unidirectional reflectionless propagation of THz waves. This suggests exciting prospects for detecting chemical and biological agents with ultrahigh sensitivity.