Microscopic Response Mechanism of Epsilon-Negative and Epsilon-Near-Zero Metacomposites

Metals have traditionally served as the primary functional phase in the development of metamaterials exhibiting epsilon-near-zero (ENZ) and epsilon-negative (EN) responses, albeit with persisting ambiguities regarding their response mechanisms. This paper presents the tunable ENZ (<i>ε</i>' ~ 0) and EN (<i>ε</i>' < 0) parameters at the 20-MHz to 1-GHz region based on Cu/CaCu₃Ti₄O₁₂ (Cu/CCTO) metacomposites. By means of first-principles calculations and multi-physics simulations, the underlying mechanisms governing ENZ and EN responses are unveiled. The intricate pathways through which metacomposites achieve 2 dielectric response mechanisms are delineated: At low Cu content, a weak EN response (|<i>ε</i>'| < 200) was excited by electric dipole resonance, accompanied by ENZ effect; conversely, at high Cu content, due to the increase in effective electron concentration, plasmonic oscillation behavior occurs in the constructed 3-dimensional Cu network, resulting in strong EN response (|<i>ε</i>'| ~ 1,000) in the radio frequency band. These phenomena are explicated through 2 distinct Cu/CCTO models: Cu in an isolated state and a connected network state. This study not only comprehensively elucidates the 2 EN response mechanisms achieved by typical metacomposites with metals as functional phases but also delves into their associated electromagnetic shielding and thermal properties, providing a theoretical basis for their practical applications.