Confinement-Induced Nonlocality and Optical Nonlinearity of Transdimensional Titanium Nitride in the Epsilon-Near-Zero Region

TL;DR

This paper demonstrates that ultrathin trans-dimensional titanium nitride films exhibit significantly enhanced optical nonlinearity near the epsilon-near-zero region, driven by electron confinement effects, with potential applications in ultrathin photonic devices.

Contribution

It introduces a nonlinear nonlocal electromagnetic response model for trans-dimensional TiN films, revealing their strong nonlinear enhancement in the ENZ region compared to conventional films.

Findings

Nearly two orders of magnitude stronger nonlinear absorption in TD TiN films near ENZ

Enhanced nonlinearity explained by a nonlinear nonlocal electromagnetic response model

Comparison with TiAlN highlights importance of low-loss ENZ response

Abstract

Ultrathin plasmonic films that approach the trans-dimensional (TD) thickness limit provide a promising route for light_matter interaction control and manipulation, yet their nonlinear optical response near the epsilon_near_zero (ENZ) condition remains poorly understood. Here, we report the strongly enhanced optical nonlinearity for their typical representative high quality TiN epitaxial films with thicknesses down to a few nanometers. Systematic Z_scan measurements reveal a pronounced increase in nonlinear absorption with decreasing thickness. Especially in the ENZ spectral region, the TD TiN films exhibit nearly two orders of magnitude stronger nonlinear absorption over a broad range of incidence angles as compared to conventional thin films. The enhanced nonlinear absorption observed is well described by a nonlinear nonlocal electromagnetic response model that accounts for electron confinement effects unique to the TD plasmonic systems. Comparison with Ti1_xAlxN highlights the necessity of low-loss ENZ response for nonlinear enhancement. These findings identify TiN and similar TD plasmonic systems as a robust refractory platform for exploiting ENZ mediated nonlinear processes in ultrathin photonic material structures.