title: Comment on "Antisymmetric resonant mode and negative refraction in double-ring resonators under normal-to-plane incidence".
abstract: In a recent paper, Ding, Liang, Zhang, Zhou, and Yuan [Phys. Rev. E 79, 016604 (2009)] reported a negative refraction of double-ring resonator structure at the normal incidence based on an intrinsical electric and an antisymmetric resonances. We argue that the antisymmetric resonance does not respond to a negative permeability, and the left-handed nature comes from the single-negative refraction rather than the double-negative one.
authors.affiliation: Department of Physics and Astronomy, K. U. Leuven, Leuven B-3001, Belgium. thanhtung.nguyen@fys.kuleuven.be
authors.forename: Nguyen Thanh
authors.initials: NT
authors.lastname: Tung