Control of Near-Field Thermal Radiation Characteristics Based on Hyperbolic Materials

This chapter focuses on the modulation of near-field thermal radiation and spontaneous emission using the unique properties of natural hyperbolic materials. It starts by investigating the spontaneous emission of quantum emitters near a single-layer plate. The study shows that the Purcell factor can be actively modulated by rotating the material's crystal axis in different planes (y–z, x–z, x–y), achieving a modulation factor as high as 400. This is attributed to the shifting excitation regions of hyperbolic phonon polaritons. The chapter then moves to parallel-plate systems, examining how substrates—both lossless and lossy—impact near-field radiative heat transfer. It clarifies the contribution of surface and bulk hyperbolic polaritons and reveals how substrate loss can either enhance or inhibit heat flux depending on the gap distance and material constants. The research further extends to multi-body systems, exploring a nanoparticle configuration where mechanical rotation is used to regulate near-field thermal conductivity, providing a method for non-contact thermal management. The underlying mechanism involves the coupling and mismatch of localized hyperbolic polaritons, which can be precisely tuned by the rotation angle, vertical displacement, and particle spacing. By elucidating these mechanisms, the chapter provides a theoretical foundation for high-precision nanoscale thermal switching and communication, emphasizing the superiority of natural hyperbolic materials in providing directional and tunable near-field interactions.