Near-field radiative modulator driven by anisotropic hyperbolic polaritons in biaxial hyperbolic materials

Abstract

α-phase molybdenum trioxide (α-MoO3) is an excellent biaxial hyperbolic material, whose thermal radiation properties depend highly on the crystal directions. The directional properties of thermal radiation can be controlled by changing the crystal directions of α-MoO3, which provides a novel path for the modulation of thermal radiation. In this work, we find that the near-field radiative heat transfer (NFRHT) between two α-MoO3 nanoparticles (NPs) mediated by an α-MoO3 planar substrate clearly depends on the crystal directions of α-MoO3. Due to the strong directionality of the localized hyperbolic polaritons in the NPs and the volume-confined hyperbolic polaritons in the substrate, we can achieve an effective modulation of the NFRHT by mechanical rotation. Numerical results show that the max modulation contrast could reach 60 when the planar substrate is a semi-infinite medium. The contribution of the vacuum, scattering, and cross terms under the influence of anisotropic NPs are analyzed separately to reveal the mechanism. Moreover, we investigate the effects of rotation angle and thickness of planar substrate on the modulation of NFRHT. Finally, we discuss the effects of rotating NPs on the performance of near-field radiative modulator. This work will guide the design of high-performance thermal radiative modulators based on anisotropic many-body systems.