  A thin metamaterial slab comprising a dielectric spacer sandwiched between a
metallic grating and a ground plane is shown to possess spatially coherent
surface resonance states that span a large frequency range and can be tuned by
structural and material parameters. They give rise to nearly perfect
angle-selective absorption and thus exhibit directional thermal emissivity.
Direct numerical simulations show that the metamaterial slab supports spatially
coherent thermal emission in a wide frequency range that is robust against
structural disorder.
