The conditions to observe and excite electromagnetic surface modes at the interface between a two-dimensional (2D) photonic crystal (PC) and bulk metal are studied. It is shown that these modes can exist in the region where bandgapsofthePCoverlapwiththeregionbelowtheplasmafrequencyofametalinthedispersi ondiagraminboth polarizations. The dispersion relation of these electromagnetic surface modes is determined numerically by con- sideringasystemofathinmetalliclayerincontactwithafinitePCofsomeperiods. Thereflectanceiscomputedby using the finite-difference time-domain (FDTD) method. With this method, it is shown that these modes can be excited and observedeven under normal incidence from a vacuum. For the studied system, the cell in contact with the metallic layer must be truncated in order to observe the interface mode. It is shown that we can select the fre- quencyofthemodeinsidethebandgapsbyproperlychoosingthetruncationparameter.
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