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# Past Events

## Magnetism and Metamaterial

Speaker: | Professor Siu-Tat Chui |

Affiliation: | Bartol Research Institute, University of Delaware, USA |

Date: | November 25, 2008 (Tue) |

Time: | 4:00-5:00 p.m. |

Venue: | Room 522, 5/F, Chong Yuet Ming Physics Building, HKU |

### Abstract:

We summarise our recent work on exploiting the magnetic degrees of freedom in photonic systems:

**Novel phenomena in magnetic photonic crystals (MPC):**

(1) Indexed matched negative refraction with only ferrite rods from the philosophy of pseudopotentials.

(2) Probing photonic states with macroscopic circulations: In reflection from MPCs, an edge like component is predicted.

(3) Magnetic surface plasmon bands: Because of the symmetry of Maxwell’s equations with respect to its magnetic and electric degrees of freedom, magnetic surface plasmons (MSP) are expected to occur when the magnetic susceptibility μ is equal to -1, similar to conventional SPs which occur at ε = -1. For a periodic array array of ferromagnets, coupled MSP states form MSP bands. The supression of transmission due to gaps around these bands can be moved with an external magnetic field and is observed experimentally.

**Design of wire structures based on an analytic solution of their resonance : **

(1) Minituration: We derived simple polynomial equations to determine the entire resonance spectra of split ring structures. For double stacking split rings made with flat wires, we showed that the resonance frequency depends linearly on the ring-ring separation. In particular, we found that the wavelength of the lowest resonance mode can be made 10^{5} times the geometrical size of the ring for realistic experimental conditions. For current systems this ratio is of the order of 10. Finite-difference-time-domain simulations on realistic structures verified the analytic predictions.

(2) Giant Faraday rotation: We extend our approach of small metallic structures to helixes. We find that under appropriate conditions, a Faraday rotation at zero field can be manifested that is three orders of magnitude higher than that of Terbium Gallium Garnet under a field of 10 Teslas.

(3) Off-diagonal magnetoelectics: The split ring systems are magnetoelectric: We find a mode such that the electric field becomes elliptically polarized with a component in the longitudinal direction. Even though the group velocity and the wave vector are parallel, the Poynting vector possesses a component perpendicular to the wave vector. The speed of light can be real even when the product εμ is negative.

Coffee and tea will be served 20 minutes prior to the seminar.