Low-temperature behavior of magnetic metamaterial elements

Periodically arranged metallic resonators can produce a negative permeability medium. However, the resonant response weakens at extreme regimes under certain conditions, which is the major problem of obtaining a negative index in the visible regime. We report that by decreasing the operation temperature, the metal conductivity can be increased, enhanced negative permeability can be obtained and the operation range of the negative permeability media, and thereby the negative index media, can be extended. We doubled the resonant strength of a typical resonator operating at microwave frequencies by decreasing its temperature to 150 K. The results are promising for the demonstration of negative index media in the visible regime.