Floquet-enhanced Thermal Emission in Silicon Carbide Avoids Divergence, Demonstrates Modest Enhancement

Floquet engineering presents a promising pathway to boost emission from materials subjected to time-varying stimuli, and researchers are now clarifying the underlying physics with a rigorous theoretical framework. Yuhua Ren, Hui Pan, and Jian-Sheng Wang, all from the National University of Singapore, have developed a unified theory to model emission from time-dependent media, specifically examining silicon carbide under modulated conditions. Their work establishes a formal connection between two key approaches, nonequilibrium Green’s function formalism and macroscopic electrodynamics, by deriving a consistent equation that governs both. This achievement resolves potential inconsistencies in modelling time-modulated materials and provides a robust foundation for predicting and optimising emission enhancements, reinforcing the potential of Floquet engineering as a versatile tool for controlling material properties.

This research clarifies the complex process of light emission from materials whose properties change over time, employing both nonequilibrium Green’s function methods and macroscopic quantum electrodynamics. The team successfully demonstrated that these two theoretical approaches are formally compatible, deriving a consistent Lippmann-Schwinger equation within each framework. This achievement provides a unified foundation for analyzing how materials emit light when their characteristics are dynamically altered, offering a deeper understanding of the underlying physics.

A central accomplishment lies in the development of methods for carefully separating the electric field into its positive and negative frequency components. The researchers established specific criteria to ensure the physical validity of these components, crucially avoiding mathematical inconsistencies and ensuring a reliable intensity spectrum. This careful approach allows for accurate modeling of the emission process and provides a robust framework for future investigations.

Time Modulation Enhances Near-Field Radiative Transfer

This research investigates how energy transfer between closely spaced objects changes when one or both materials have properties that vary with time. The team focused on time-modulated materials and employed advanced theoretical techniques to understand the behavior of energy transfer in the near field, where conventional models break down. By combining nonequilibrium Green’s function methods, macroscopic quantum electrodynamics, and Floquet engineering, they developed a comprehensive framework for analyzing these complex systems.

The researchers demonstrated that both nonequilibrium Green’s function and macroscopic quantum electrodynamic approaches yield the same fundamental equation, confirming the consistency of their theoretical framework. They also carefully defined the positive and negative frequency components of the electric field, establishing criteria that avoid mathematical divergences and ensure physically meaningful results.

Numerical simulations validated the theoretical predictions, revealing that while time modulation can influence near-field radiative transfer, the resulting enhancement in energy transfer remains modest under the conditions studied. This finding suggests that while time modulation holds promise for controlling energy transfer, significant enhancements may require exploring different material properties or system configurations.

Unified Theory of Time-Dependent Light Emission

This research presents a comprehensive theoretical framework for understanding light emission from materials whose properties change over time. By combining nonequilibrium Green’s function methods and macroscopic quantum electrodynamics, the team developed a unified approach that accurately models the complex interplay between light and matter in dynamically changing systems. This framework provides a powerful tool for predicting and controlling light emission in a wide range of applications.

The team successfully demonstrated the formal compatibility of these two theoretical approaches, deriving a consistent Lippmann-Schwinger equation within both formalisms. They also developed methods for decomposing the electric field into its positive and negative frequency components, establishing criteria for physical consistency and avoiding mathematical divergence in the intensity spectrum.

The results indicate that while spectral enhancement is possible through time modulation, it remains modest under the conditions studied. Importantly, the work provides a robust foundation for understanding emission dynamics in systems where material properties change over time, reinforcing the potential of Floquet engineering as a versatile tool for tailoring light-matter interactions. Future work could extend these findings to consider the impact of material losses and nonlinear effects, potentially unlocking more substantial enhancements in emission intensity and paving the way for novel photonic devices.