We report observations of superradiance for atoms trapped in the near field of a photonic crystal waveguide (PCW). By fabricating the PCW with a band edge near the D1 transition of atomic cesium, strong interaction is achieved between trapped atoms and guided-mode photons. Following short-pulse excitation, we record the decay of guided-mode emission and find a superradiant emission rate scaling as Γ¯SR-N¯Γ1D for average atom number 0.19N¯ 2.6 atoms, where Γ1D/Γ′=1.0±0.1 is the peak single-atom radiative decay rate into the PCW guided mode, and Γ′ is the radiative decay rate into all the other channels. These advances provide new tools for investigations of photon-mediated atom-atom interactions in the many-body regime.
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