Narrow-linewidth circular dichroism in asymmetric double split ring resonator metasurface

Strong and narrow-linewidth circular dichroism (CD) spectroscopy promises potential applications in bio-chemical sensing and detection of the weak chirality in natural molecules. Here we proposed a chiral metasurface formed by the asymmetric metal double split ring resonator (DSRR) arrays, the circular dichroism (CD) of which has been investigated. The maximum CD for absorption response of the metasurface can reach 0.61 with an ultra-narrow spectral linewidth of 9.6 nm in the mid-infrared (MIR) band. Our calculation results show that the chiral metasurface can support two surface lattice resonance modes for the left circularly polarized (LCP) and right circularly polarized (RCP) light. The narrow linewidth of CD is enabled by the spin-selective high-Q resonance modes with a differential absorptivity for LCP and RCP light. Our findings shed light on the potential applications in spin-selective perfect optical absorption, high-sensitive polarization detection, and chirality sensing.