Natural Negative-Refractive-Index Materials

TL;DR

This paper predicts that Dirac semimetals can exhibit negative refractive index due to quantum effects and their unique electronic structure, extending NRI phenomena beyond traditional metamaterials and into new material classes.

Contribution

It introduces the novel prediction that Dirac semimetals can host negative refractive index phenomena driven by quantum vacuum polarization effects.

Findings

NRI can occur in Dirac semimetals due to quantum effects.

NRI manifests over a broad frequency range, observable near GHz frequencies.

The phenomenon is temperature-dependent and linked to Dirac cone structures.

Abstract

Our calculation shows that negative refractive index (NRI), which was known to exist only in metamaterials in the past, can be found in Dirac semimetals (DSM). Electrons in DSM have zero effective mass and hence the system carries no nominal energy scale. Therefore, unlike those of ordinary materials, the electromagnetic responses of the electrons in DSM will not be overwhelmed by the physical effects related to electron mass. NRI is induced by the combination of the quantum effect of vacuum polarization and its finite temperature correction which is proportional to $T^4$ at low temperature. It is a phenomenon of resonance between the incident light and the unique structure of Dirac cones, which allows numerous states to participate in electron-hole pair production excited by the incident light with similar dispersion relation to that of Dirac cones. NRI phenomenon of DSM manifests in an extensive range of photon frequency and wave number and can be observed around giga Hertz range at temperature slightly higher than room temperature.