Near‐Field Coupling Induced Less Chiral Responses in Chiral Metamaterials for Surface‐Enhanced Vibrational Circular Dichroism

Abstract Chiral metamaterials play vital roles in manipulating the circular polarization of electromagnetic waves. Although planar chiral metamaterials are believed to have no true/intrinsic chirality, the design of structural anisotropy can still create enormous circular dichroism, while the mechanism is fully explored. Here, for the first time, it is observed that strong near‐field coupling induces less chiral response in chiral metamaterials. Selective exposure methods to manipulate the near‐field coupling strength, and experimentally validate the circular dichroism difference from tailored near‐field coupling effect are leveraged, which provides strong evidence for the assumption and can be utilized for the structural design framework. Besides, using the enhanced near‐field (over 750‐fold), surface‐enhanced vibrational circular dichroism (SEVCD) for glucose enantiomers, which shows a larger‐than‐one normalized sensitivity compared with metamaterials with chiral response is demonstrated. Furthermore, The potential of SEVCD by detecting a broadband signal using arrayed metamaterials is explored. These findings pave the way toward chiroptical nanophotonic designs for potential biomedical and healthcare applications.