Strange metallic plasmons and optical conductivity in La2−xCaxCuO4 and WTe2

We derive the required formalism to evaluate the complex (frequency-dependent) dielectric function and optical conductivity to capture their changes due to doping, temperature and frequency. Subsequently, we apply our microscopic theory to the experimental data obtained from La\(_{2-x}\)Ca\(_{x}\)CuO\(_{4}\) superconductor and semimetallic WTe\(_2\) to derive the physical mechanisms of complex dielectric and optical conductivity. We find that the frequency-dependent optical conductivity function that changes as a result of doping, temperature and frequency is influenced by the plasmon density, plasmon-plasmon and plasmon-polariton scattering rates. However, for the semiconducting La\(_{2}\)CuO\(_{4}\) compound, plasmon density is the dominant contributor to optical conductivity, prior to scattering rate effect at a higher frequency range. In addition, the plasmon density and the stated scattering rates are found to vary distinctly at different frequency ranges, which define the optical conductivity curves for La\(_{2-x}\)Ca\(_{x}\)CuO\(_{4}\) and WTe\(_2\) when the temperature, chemical composition and photon energy are systematically varied. As usual, we find that the effects of temperature, Ca-doping and changing frequency on optical conductivity data consistently obey the physics derived from the Ionization Energy Theory (IET) and its method.