Session: K9-05: RADIATIVE COOLING AND RADIATIVE PROPERTIES OF NANOMATERIALS

Paper Number: 138712

138712 - Controlling the Contrast Between Absorptivity and Emissivity in Nonreciprocal Thermal Emitters 

Abstract: 

Recent advancements in nonreciprocal thermal emitters challenge the conventional Kirchhoff's law, which states that emissivity and absorptivity should be equal for a given direction, frequency, and polarization. These emitters can break Kirchhoff's law and enable unprecedented thermal photon control capabilities. However, current studies mainly focus on increasing the magnitude of the contrast between emissivity and absorptivity, with little attention paid to how the sign or bandwidth of the contrast may be controlled. In this work, we show such control ability can be achieved by coupling resonances that can provide opposite contrasts between emissivity and absorptivity.

We define the contrast between a and e, as h = a - e, which is a key figure of merit in nonreciprocal emitters. In reciprocal emitters, which follow Kirkoff’s law of thermal radiation, it is guaranteed that h = 0. For nonreciprocal emitters, h is nonzero and can vary between -1 to 1. The magnitude of the contrast | h | indicates degree of violation of Kirchhoff's law, whereas the sign of h directly controls the photon transport behavior. In this work, we implement temporal coupled-mode theory to propose a method to control the sign of h by coupling two modes that can provide opposite contrasts between emissivity and absorptivity. By coupling modes that can yield opposite signs for , one can effectively control the bandwidth, the direction, the sign, and also the magnitude of the contrast between absorptivity and emissivity. We begin with an exemplary system comprising two layers of magnetic Weyl semimetals, each layer having Weyl nodes separated in antiparallel directions, leading to opposite Brewster modes. We demonstrate that by merging these two modes, the sign of h can be manipulated, offering an advantage over a system with a single layer of magnetic Weyl semimetal. Additionally, we explore a magneto-optical system with multiple layers of InAs. By incorporating a dielectric layer, we show that the resultant Fabry-Perot resonances can be utilized to adjust both the sign and bandwidth of h.

Extensive efforts are ongoing to increase the magnitude of  in nonreciprocal emitters. The integration of these efforts with the methodology described in this study can significantly enhance the ability to fine tune nonreciprocal radiative properties for a wide range of applications, representing a substantial step forward in nonreciprocal thermal photonics.

Acknowledgements: This research was supported by the start-up funding from the University of Houston and the funding from National Science Foundation under grant no. CBET-2314210. The authors are grateful for the support of the Research Computing Data Core at the University of Houston for assistance with the calculations carried out in this work.

 

 

Presenting Author: Sina Jafari Ghalekohneh University of Houston

Presenting Author Biography: PhD Candidate, Department of Mechanical Engineering, University of Houston

Authors:

Sina Jafari Ghalekohneh University of Houston
Changkang Du University of Houston
Bo Zhao University of Houston