title: Comment on "Superwide-band negative refraction of a symmetrical E-shaped metamaterial with two electromagnetic resonances".
abstract: The metamaterial presented by Yan [Phys. Rev. E 77, 056604 (2008)] is claimed to exhibit a superwide band of negative refraction. However, a retrieval procedure of the refractive index including the phase advance of a propagating plane wave shows that the material provides two distinct narrow bands with a negative refractive index instead of a single superwide band and thus the central claim of the paper is incorrect.
authors.affiliation: Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, Kaiserslautern, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Paul
authors.forename: René
authors.initials: R
authors.lastname: Beigang
authors.forename: Marco
authors.initials: M
authors.lastname: Rahm