Plasmon-Matter Interactions in Optoelectronic Metamaterials with Negative Refractive Index

Optoelectronic metamaterials composed of nanoscale metallic structures and semiconductor quantum structures constitute a powerful platform to explore light-matter interaction and new devices. In this work, we numerically study an optoelectronically coupled metamaterial consisting of metallic double fishnet (DF) layers and semiconductor quantum well (QW) spacing layer. When the electronic intersubband transition (ISBT) in the QW coincides with the plasmonic resonances of the DF structure, the plasmon-matter interaction (PMI) can modify the optical properties considerably. In case of the ISBT-matching localized surface plasmons (LSP), i.e., fQW = fLSP, the polarization-selection-rule forbidden ISBT absorption can be enabled due to the nonnegligible Ez field distributions while the retrieved optical constants remain almost unchanged. However, when the gap surface plasmons (GSP) are matched, i.e., fQW = fGSP, PMI exhibits a clear anti-crossing behavior implying strong coupling effects between ISBT and GSP resonance and formation of intersubband polaritons. The effective optical constants are therefore modulated appreciably. The large difference between GSP and LSP can be attributed to their distinctive resonance qualities (Q-factors) and polarization conversion ratios (99.28 % for GSP and 1.54 % for LSP) from the transverse electric (TE) to transverse magnetic (TM) mode. Our results provide insight into the physical mechanism of PMI in nanoscale semiconductor-plasmon hybrid systems and suggest an alternative means in tunable negative refractive index (NRI) applications.