Negative Effective Mass in Plasmonic Systems

We report the negative effective mass (density) metamaterials based on the electro-mechanical coupling exploiting plasma oscillations of a free electron gas. The negative mass appears as a result of the vibration of a metallic particle with a frequency of ω, which is close the frequency of the plasma oscillations of the electron gas [Formula: see text] relative to the ionic lattice [Formula: see text]. The plasma oscillations are represented with the elastic spring [Formula: see text] , where [Formula: see text] is the plasma frequency. Thus, the metallic particle vibrated with the external frequency ω is described by the effective mass [Formula: see text] , which is negative when the frequency [Formula: see text] approaches [Formula: see text] from above. The idea is exemplified with two conducting metals, namely Au and Li.