Epsilon-Near-Zero Metamaterials with Phase-Change Materials for Active Optical Responses

Epsilon-Near-Zero (ENZ) metamaterials have emerged as a powerful tool for manipulating light-matter interactions, offering unprecedented phenomena such as wave-front shaping, optical tunneling, and great enhancement of local fields due to their vanishing refractive index. However, conventional plasmonic ENZ structures are intrinsically static, limiting their applicability in optoelectronic devices. This thesis investigates an active ENZ platform based on multilayered nanostructures combining noble metals with phase-change materials, specifically Vanadium Dioxide. By exploiting the first-order Insulator-to-Metal Transition (IMT) of VO2 at a critical temperature of T=68°C, the effective dielectric function of the metamaterial can be dynamically tuned, shifting the ENZ wavelength across the near-infrared and visible spectrum. The design of the multilayered material is carried out using the Effective Medium Approximation (EMA) framework to theoretically map and identify the tunability range of the ENZ wavelength, and Transfer Matrix and Finite Element Method (FEM) simulations are performed in order to correlate the ENZ wavelength with optical measurements. Special emphasis is placed on the transformation of the Local Density of Optical States (LDOS) and the resulting modification of the spontaneous emission rate (Purcell effect). The transition from the low-loss monoclinic insulating phase to the highly lossy, strongly correlated rutile metallic phase of VO2 reveals a complex trade-off: while the metallic transition opens high k momentum channels that boost the total Purcell factor, it introduces non-negligible Ohmic dissipation, leading to near-field quenching. By optimizing the geometry and filling fraction of the metamaterial, this work aims to investigate how the phase change properties of VO2 can be used to tune the radiative emission rate of single photon emitters.