Simultaneous Broadband Nonreciprocal Thermal Emission for Transverse Magnetic and Electric Polarizations.

Objects violating Kirchhoff's law of thermal radiation exhibit unequal absorptivity or emissivity at symmetrical polar angles relative to the normal direction, providing prerequisites for approaching thermodynamic limits in radiative cooling and photon energy conversion, such as the Landsberg limit. Previous studies have demonstrated that broadband nonreciprocal thermal radiation (NTR) can be achieved using magnetized epsilon-near-zero (ENZ) materials, such as InAs or Weyl semimetals (WSMs), overcoming the narrowband limitations of most conventional NTR emitters. However, constrained by the inherent properties of magnetized materials, significant broadband NTR is only realized under transverse magnetic mode, fundamentally limits the thermodynamic efficiency under dual-polarization conditions. This work combines multilayer gradient ENZ WSMs with metasurface geometric construction to achieve, for the first time, significant broadband (8-14 μm) NTR in both transverse magnetic and transverse electric modes. It also exhibits robustness to incident waves directionality. This structure achieves strong nonreciprocity of absorptivity and emissivity under dual-polarization. The performance is enabled by the geometric asymmetry inducing polarization conversion to overcome polarization mismatch, whereas the magnetized ENZ WSMs fundamentally break Lorentz reciprocity. This research further advances the development of broadband NTR under multipolarization conditions and can be extended to other magnetized metals, III-V semiconductors, magnetized ENZ metamaterials, and metasurfaces.