Thermally stable negative permittivity and fano like resonance in multi-doped manganite

We report an atypical dielectric behavior of a newly synthesized A-site multi-doped La 0.4 Bi 0.3 Sr 0.2 Ba 0.1 MnO 3 manganite, which has not been reported previously. The material exhibits a thermally robust negative real permittivity across a broad frequency (10KHz-100MHz) and temperature range (230K–400K). This is interpreted as result of a collective plasmonic state of free electrons and modeled according to the Drude formalism. Dielectric losses exhibit exceptionally low values and tanδ reaches notable minima (0.0002<tanδ<0.01). A striking feature is a double zero-crossing of real permittivity around 40MHz which emerges from the interplay between slow interfacial polarization and fast grain response. This previously unreported phenomenon , in single-phase manganites, suggests a Fano-Like resonance modeled according to the Lorentz-Drude formalism. Furthermore, the imaginary permittivity exhibits negative values at high frequencies, a phenomenon rarely observed in natural materials. These combined phenomena, unprecedented in this material class, position La 0.4 Bi 0.3 Sr 0.2 Ba 0.1 MnO 3 as a unique functional oxide with high potential for applications in metamaterials, near-zero permittivity structures, and electromagnetic wave modulators. • Broadband and thermally stable negative permittivity over 230–400 K. • Fano-like dielectric resonance identified around 40 MHz. • Exceptionally low dielectric losses (0.0002<tanδ< 0.01). • Plasmonic behavior was successfully modeled through the Drude and Lorentz-Drude formalism. • Negative ε″ at high frequencies suggesting effective inductive behavior and possible magnetoelectric coupling.