Near-complete violation of Kirchhoff s law in thermal radiation in ultrathin magnetic Weyl semimetal films

TL;DR

This study demonstrates that ultrathin magnetic Weyl semimetal films can significantly violate Kirchhoff's law in thermal radiation, offering a simple and experimentally feasible way to engineer nonreciprocal thermal emitters.

Contribution

The paper introduces a novel approach using ultrathin magnetic Weyl semimetal films to achieve strong nonreciprocal thermal radiation, surpassing previous thicker and more complex designs.

Findings

Achieved strong nonreciprocal radiation at 9.15 μm with 100 nm thick MWSM film.

Enhanced nonreciprocity due to Fabry-Perot resonances.

Proposed structure is easier to fabricate for experimental verification.

Abstract

The ability to break Kirchhoff s law is of fundamental importance in thermal radiation. Various nonreciprocal emitters have been proposed to break the balance between absorption and emission. However, the thicknesses of the nonreciprocal materials are usually larger than 1/10 times of the wavelength. Besides, the previous proposed nonreciprocal emitters are complex, thus they can hardly be fabricated in experiment to verify the Kirchhoff s law for nonreciprocal materials. In this paper, we investigate the nonreciprocal thermal radiation of the magnetic Weyl semimetal (MWSM) film atop of the metal substrate. It is found that the strong nonreciprocal radiation at the wavelength of 9.15 {\mu}m can be achieved when the thickness of the MWSM film is 100 nm. The enhanced nonreciprocity is attributed to the Fabry-Perot resonances. The results indicate that the MWSM film is the promising candidate to engineer the ultrathin and simple nonreciprocal thermal emitters. What is perhaps most intriguing here is that the proposed structure can be more easily fabricated in experiment to verify the Kirchhoff s law for nonreciprocal materials.