Negative Correlation Between Thermal and Electrical Conductivity in Epsilon‐Negative Nanocomposites

Abstract Epsilon‐negative materials (ENMs) hold promise for the advancement of the next generation of electronic devices. Most epsilon‐negative materials strongly correlate with metal properties, which limits their applications in electronic packaging. Instead, achieving a negative permittivity in the insulating state is expected to show the decoupling of electrical and thermal conductivities, and experimental demonstration of this behavior is lacking. In this study, multi‐walled carbon nanotubes (MWCNTs)@polydopamine (PDA)‐silver/polyimide (PI) nanocomposites are engineered to achieve weakly negative permittivity, which is attributed to the localized plasma oscillations. The PDA layer and nano‐Ag are exploited to confine electrons with MWCNTs for improving energy transport while perturbing directional current, thereby realizing high thermal conductivity and low electrical conductivity. This work provides insights into the fundamental nature of heat and charge transport in epsilon‐negative systems.