Theory of epsilon-near-zero modes in ultrathin films

The physics of the epsilon-near-zero (ENZ) mode, which is supported by a nanolayer at the frequency where the dielectric permittivity vanishes, has recently been a subject of debate. In this Rapid Communication, we thoroughly investigate and clarify the physics of this mode, providing its main characteristics and its domain of existence. This understanding will benefit all the applications that rely on ENZ modes in semiconductor nanolayers, including directional perfect absorption, voltage-tunable devices, and ultrafast thermal emission.