Axion-Field-Enabled Nonreciprocal Thermal Radiation in Weyl Semimetals

Abstract

Objects around us constantly emit and absorb thermal radiation [1][2][3][4][5][6]. The emission and absorption processes are governed by two fundamental radiative properties: emissivity and absorptivity. For reciprocal systems, the emissivity and absorptivity are restricted to be equal by Kirchhoff's law of thermal radiation [1,2,7]. This restriction limits the degree of freedom to control thermal radiation and contributes to an intrinsic loss mechanism in photonic energy harvesting systems such as solar cells [8]. Existing approaches to violate Kirchhoff's law typically utilize conventional magnetooptical effects in the presence of an external magnetic field [9,10]. However, these approaches require either a strong magnetic field (∼3T) [9], or narrow-band resonances under a moderate magnetic field (∼0.3T) [10], because the non-reciprocity in conventional magneto-optical effects is usually weak in the thermal wavelength range. Here, we show that the axion electrodynamics in magnetic Weyl semimetals can be used to construct strongly nonreciprocal thermal emitters that near completely violate Kirchhoffs law over broad angular and frequency ranges, without requiring any external magnetic field. The non-reciprocity moreover is strongly temperature tunable, open new possibilities for active non-reciprocal devices in controlling thermal radiation.[1] G. Kirchhoff, Ueber das Verhältniss zwischen dem Emissionsvermögen und dem Absorptionsvermögen der Körper für Wärme und Licht, Annalen der Physik 185, 275 (1860).

Sub‐Wavelength Passive Optical Isolators Using Photonic Structures Based on Weyl Semimetals

“…In the context of photonic applications, Weyl semimetals have been proposed recently for generation of nonreciprocal surface plasmons and design of nonreciprocal thermal emitters. [ 40–42 ]…”

Hexagonal Zr3X (X = Al, Ga, In) Metals: High Dynamic Stability, Nodal Loop, and Perfect Nodal Surface States

“…The dimensionality of band-crossings is a criterion used to classify topological semimetals/metals. The most famous topological semimetals/metals with zero-dimensional band-crossings, i.e., zero-dimensional nodal points, are Dirac semimetals/metals (Chen et al, 2015(Chen et al, , 2020Bradlyn et al, 2017;Zhong et al, 2017;Jing and Heine, 2018;Liu et al, 2018b;Zhang et al, 2018b;Khoury et al, 2019;Wang et al, 2020f;Xu et al, 2020) and Weyl semimetals/metals (Peng et al, 2016;Lin et al, 2017;Fu et al, 2018;Zhang et al, 2018c;Zhou et al, 2019;Gupta et al, 2020;Jia et al, 2020;Liu et al, 2020;Meng L. et al, 2020;Zhao B. et al, 2020). We selected Weyl semimetals/metals as examples here because there exists a band-crossing of the valance band and conduction band at an isolated nodal point in the momentum space of these solids.…”

Up‐And‐Coming Advances in Optical and Microwave Nonreciprocity: From Classical to Quantum Realm

“…Further investigation in the area of nonreciprocal devices based on magnetic field bias is mainly focused on new materials such as WSs [ 127–130 ] ( Figure a,b), metamaterials and metasurfaces [ 131,132 ] (Figure 3c), magnetic 2D materials and heterostructures [ 133 ] (Figure 3d), new non‐linear ferroelectric materials, [ 134–136 ] and topological insulators [ 137,138 ] (Figure 3e,f). In this section, we briefly overview these important research areas with a focus on their nonreciprocal response.…”

“…In the realm of light absorption and (thermal) emission, the reciprocity principle is expressed by Kirchhoff's law of thermal radiation that dictates that for reciprocal systems, the emissivity and absorptivity are restricted to be equal. [ 83,154 ] In recent work, however, it has been reported that nonreciprocal thermal emitters can be realized using topological magnetic WSs [ 128 ] that do not require strong magnetic fields (≈0.3–3 T) as in other existing approaches based on conventional magneto‐optical effects. [ 155,156 ] The authors predict Kirchhoff's law's violation in a broad angular and frequency range and its high temperature‐sensitivity.…”