title: Direct observation of negative-index microwave surface waves.
abstract: Waves propagating in a negative-index material have wave-front propagation (wavevector, k) opposite in direction to that of energy flow (Poynting vector, S). Here we present an experimental realisation at microwave frequencies of an analogous surface wave phenomenon whereby a metasurface supports a surface mode that has two possible wavevector eigenstates within a narrow band of frequencies: one that supports surface waves with positive mode index, and another that supports surface waves with negative mode index. Phase sensitive measurements of the near-field of surface waves across the metasurface show the contrasting spatial evolution of the two eigenstates, providing a unique opportunity to directly observe the negative-index phenomenon.
authors.affiliation: Electromagnetic and Acoustic Materials Group, Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK.
authors.forename: J A
authors.initials: JA
authors.lastname: Dockrey
authors.affiliation: Electromagnetic and Acoustic Materials Group, Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK.
authors.forename: S A R
authors.initials: SA
authors.lastname: Horsley
authors.affiliation: Electromagnetic and Acoustic Materials Group, Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK.
authors.forename: I R
authors.initials: IR
authors.lastname: Hooper
authors.affiliation: Electromagnetic and Acoustic Materials Group, Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK.
authors.forename: J R
authors.initials: JR
authors.lastname: Sambles
authors.affiliation: Electromagnetic and Acoustic Materials Group, Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK.
authors.forename: A P
authors.initials: AP
authors.lastname: Hibbins