  The concept of the broadband epsilon-near-zero meta-atom consisting of
layered stacks with specified metallic filling ratio and thickness is proposed
based on the Bergman spectral representation of the effective permittivity. The
step-like metal-dielectric multilayer structures are designed to achieve
realistic broadband epsilon-near-zero meta-atoms in optical frequency range.
These meta-atoms can be integrated as building blocks for unconventional
optical components with exotic electromagnetic properties over a wide frequency
range, such as the demonstrated broadband directional emission and phase front
shaping.
