  We numerically demonstrate that a planar slab made of magnetic Weyl semimetal
(a class of topological materials) can emit high-purity circularly polarized
(CP) thermal radiation over a broad mid- and long-wave infrared wavelength
range for a significant portion of its emission solid angle. This effect
fundamentally arises from the strong infrared gyrotropy or nonreciprocity of
these materials which primarily depends on the momentum separation between Weyl
nodes in the band structure. We clarify the dependence of this effect on the
underlying physical parameters and highlight that the spectral bandwidth of CP
thermal emission increases with increasing momentum separation between the Weyl
nodes. We also demonstrate using recently developed thermal discrete dipole
approximation (TDDA) computational method that finite-size bodies of magnetic
Weyl semimetals can emit spectrally broadband CP thermal light, albeit over
smaller portion of the emission solid angle compared to the planar slabs. Our
work identifies unique fundamental and technological prospects of magnetic Weyl
semimetals for engineering thermal radiation and designing efficient CP light
sources.
