Nonlinear epsilon-near-zero materials explained: opinion

Epsilon-near-zero materials have recently come onto the scene as promising new nonlinear optical materials. However, this field is quite crowded and it is prudent to ask whether they possess any key features which will elevate them above other candidates. It is our opinion that they in fact possess two such features, a simultaneous intrinsic and extrinsic enhancement to light matter interaction. Here we elucidate these enhancement mechanisms and compare them to other manifestations found in literature, explaining why this combination is unique to epsilon-near-zero materials.