Multi-state Reconfigurable Nonreciprocal Thermal Emitter Driven by VO2 and Ge2Sb2Te5

Nonreciprocal thermal radiation (NTR) holds promising potential across various domains, including photovoltaic systems, radiation cooling, and energy conversion devices. Yet, the investigation into dynamically tunable NTR remains underdeveloped, particularly concerning multiple states. In this work, we have conceptualized and demonstrated a multi-state reconfigurable nonreciprocal thermal emitter through combining Weyl semimetals with two distinct phase change materials. Within the GST/VO2/Weyl/Ag multilayer thin-film structure, we have successfully achieved 4-state NTR at a specified wavelength of 8.85 μm. Specifically, when the GST remains in the amorphous state and VO2 transitions from its insulating state to the metallic state, the difference (η) between the absorption and emission is 0.93 and -0.03, respectively, essentially realizing the "on" and "off" states. Subsequently, when VO2 is sustained in its metallic state, the GST undergoes a phase change, resulting in two intermediate states of NTR. Weyl semimetals break the Lorentz reciprocity, providing the potential to challenge the traditional Kirchhoff's law. The distinct NTR states observed are attributed to the independent structural phase transitions of VO2 and GST occurring at different temperatures. This evidence is substantiated through the analysis of electric field distributions and material loss. By varying the positions of the phase change materials and Weyl semimetals, we achieve stepwise modulation of the NTR at wavelengths 7.07 μm and 8.93 μm, respectively. Intriguingly, a flip in the sign of η is observed. This work not only establishes a pathway for reconfigurable NTR, but also holds promise for enhancing energy collection and conversion efficiency.