Experimental realization of breaking diffraction limit by planar negative-index metamaterials in free spaceJ.-S. Lih, Y.-S. Wang, M.-C. Lu, Y.-C. Huang, K.-H. Chen, J.-L. Chern and L.-E. LiEurophys. Lett., 69 4 (2005) 544-548DOI: https://doi.org/10.1209/epl/i2004-10385-0