Strongly Enhanced Raman Optical Activity in Molecules by Magnetic Response of Nanoparticles

An analytical theory for the surface-enhanced Raman optical activity (SEROA) with the magnetic response of the substrate particle has been presented. We have demonstrated that the SEROA signal is proportional to the magnetic polarizability of the substrate particle, which can be significantly enhanced due to the existence of the magnetic response. At the same time, a large circular intensity difference (CID) for the SEROA can also be achieved in the presence of the magnetic response. Taking Si nanoparticles as examples, we have found that the CID enhanced by a Si nanoparticle is 10 times larger than that of Au. Furthermore, when the molecule is located in the hotspot of a Si dimer, CID can be 60 times larger. The phenomena originate from large magnetic fields concentrated near the nanoparticle and boosted magnetic dipole emission of the molecule. The symmetric breaking of the electric fields caused by the magnetic dipole response of the nanoparticle also plays an important role. Our findings provide a new way to tailor the Raman optical activity by designing metamaterials with the strong magnetic response.