Spin-state modulation for tunable metasurfaces

This work presents the development and characterization of tunable metasurfaces fabricated using novel phase-change materials based on spin crossover (SCO) behavior. Spin crossover materials offer a unique platform for active control of optical properties due to their ability to switch between low-spin and high-spin states under external stimuli such as temperature, pressure, or light. Moreover, these transitions are accompanied by variations in structural (volume), magnetic, electrical properties, and color. By integrating these SCO materials in the form of nanoparticles (NPs) into metasurface architectures, we investigate the dynamic tuning of optical responses across the infrared (IR) range. We demonstrate that these hybrid metasurfaces exhibit significant modulation of transmission, reflection, and phase shifts, which are controlled through reversible phase transitions induced by spin state changes. We also investigate the thermal and optical stability of single SCO-NPs and explore their potential applications in reconfigurable photonic devices, including optical switches operating in the IR regime. Our results highlight the promise of SCO nanomaterials in advancing the capabilities of metasurfaces, offering new opportunities for tunable, energy-efficient, and multifunctional nanophotonic platforms.