Momentum considerations inside near-zero index materials

TL;DR

This paper investigates momentum exchange in near-zero-index materials, revealing how different types influence light-matter interactions and the implications for fundamental processes and applications.

Contribution

It introduces a comprehensive analysis of momentum considerations in NZI materials, clarifying the Abraham-Minkowski debate and their effects on radiative processes.

Findings

Minkowski momentum is zero in all NZI categories.

Abraham momentum is zero in ENZ and MNZ, nonzero in EMNZ.

Momentum recoil and related effects are inhibited in NZI materials.

Abstract

Near-zero-index (NZI) materials, i.e. materials having a phase refractive index close to zero, are known to enhance or inhibit light-matter interactions. Most theoretical derivations of fundamental radiative processes rely on energetic considerations and detailed balance equations, but not on momentum considerations. Because momentum exchange should also be incorporated into theoretical models, we investigate momentum inside the three categories of NZI materials, i.e. inside epsilon-and-mu near-zero (EMNZ), epsilon-near-zero (ENZ) and mu-near-zero (MNZ) materials. In the context of Abraham-Minkowski debate in dispersive materials, we show that Minkowski-canonical momentum of light is zero inside all categories of NZI materials while Abraham-kinetic momentum of light is zero in ENZ and MNZ materials but nonzero inside EMNZ materials. We theoretically demonstrate that momentum recoil, transfer momentum from the field to the atom and Doppler shift are inhibited in NZI materials. Fundamental radiative processes inhibition is also explained due to those momentum considerations inside three-dimensional NZI materials. Lastly, absence of diffraction pattern in slits experiments is seen as a consequence of zero Minkowski momentum. Those findings are appealing for a better understanding of fundamental light-matter interactions at the nanoscale as well as for lasing applications.