Nanofabricated media with negative permeability at visible frequencies

We report a nanofabricated medium made of electromagnetically coupled pairs of gold dots with geometry carefully designed at a 10-nm level. The medium exhibits strong magnetic response at visible-light frequencies, including bands with negative \mu. The magnetism arises due to the excitation of quadrupole plasmon resonances. Our approach shows for the first time the feasibility of magnetism at optical frequencies and paves a way towards magnetic and left-handed components for visible optics.