Fig. 2. Spinning thermal radiation and microscopic mechanisms.

(A) Schematic of the designed metasurface with F-shape meta-atoms, where both the inversion and mirror symmetries are broken in the pseudo-2D system. (B) The measured LCP (σ+) and RCP (σ−) emissivity (solid) of the fabricated devices. They show good agreement with the simulation results (dashed). Inset: Scanning electron microscopy imaging of the fabricated device. Scale bar, 10 μm. The results directly demonstrate that spin degeneracy is removed, and the symmetry-broken metasurface imparts spin coherence in the incoherent thermal fluctuations. (C) Stokes parameters show the full polarization state (shaded areas represent the SD values of the measurements). The fabricated device presents a high S₃ peak at 7 μm, while the S₁ and S₂ are close to zero. Inset: Representation of the polarization state in the Poincaré sphere. (D) S₀ and DoP demonstrate the total intensity and the polarization purity of the thermal radiation signal (shaded areas represent the SD values of the measurements). S₀ is compared with the blackbody radiation spectrum (dashed) at the measurement temperature (492.3 K). (E) The time-averaged electric field strength (normalized by the field E₀ of incident waves) at 7 μm under LCP (left) and RCP (right) excitations. The fields are plotted along the XY (top) and XZ (bottom) planes, respectively. (F) Local emissivity density of LCP (left) and RCP radiation (right) in the meta-atom. Evident enhancement is observed for LCP radiation. (F) indicates that the spinning thermal radiation arises from the intrinsic local chirality of the metasurface.