Resumo: The quantum responses of relativistic gases of fermions or bosons to electromagnetic fields exhibit rather special properties as we vary physical parameters:

i) left-handed material behavior for low frequencies;
ii) propagation without loss of photonic modes, besides longitudinal and transverse plasmons;
iii) presence of rotonlike structures in the condensed phase of Bose gases; and
iv) quantum shifts in the temperature and pressure of Bose-Einstein condensation.

Those results were obtained using the field-theoretic framework of quantum electrodynamics, and appear in the Ph. D. thesis of Daniel Medeiros Reis.