Broadband and Wide Angle Nonreciprocal Thermal Emission from Weyl Semimetal Structures

TL;DR

This paper proposes novel Weyl semimetal-based structures that achieve broadband, wide-angle nonreciprocal thermal emission, overcoming previous limitations and enabling advanced thermal energy harvesting applications.

Contribution

It introduces three new structures combining Weyl semimetal films with dielectric and metallic layers for broadband, wide-angle nonreciprocal thermal emission without patterning.

Findings

Bandwidth of nonreciprocity is tunable via film thickness.

Dielectric spacer broadens the emission bandwidth.

Adding metallic layers enhances control over thermal radiation.

Abstract

Nonreciprocal thermal emission is a cutting-edge technology that enables fundamental control over thermal radiation and has exciting applications in thermal energy harvesting. However, so far one of the foremost challenges is making nonreciprocal emission to operate over a broad wavelength range and for multiple angles. In this work, we solve this outstanding problem by proposing three different types of structures always utilizing only one Weyl semimetal (WSM) thin film combined with one or two additional dielectric or metallic layers and terminated by a metallic substrate. First a tradeoff relationship between the magnitude and bandwidth of the thermal nonreciprocity contrast is established based on the thickness of the WSM film. Then, the bandwidth broadening effect is demonstrated via the insertion of a dielectric spacer layer that can also be fine-tuned by varying its thickness. Finally, further control on the resulting strong nonreciprocal thermal radiation is demonstrated by the addition of a thin metallic layer in the proposed few layer designs. The presented composite structures work for a broad frequency range and multiple emission angles, consisting highly advantageous properties to various nonreciprocal thermal radiation applications. Moreover, the proposed designs do not require any patterning and can be experimentally realized by simple deposition fabrication methods. They are expected to aid in the creation of broadband nonreciprocal thermal emitters that can find applications in new energy harvesting devices.