Thin-Film Radiative Thermal Diode with Large Rectification

We propose a mechanism to substantially rectify radiative heat flow by having one side of the thermal diode offering large contrast in local density electromagnetic states, while opposite serving as narrow bandpass filter that limits transport desired spectral range. To demonstrate, we realize such scenario matching thin films metal-to-insulator transition materials and polar dielectrics near field. By leveraging distinct scaling behaviors states with film thickness for metals insulators, theoretically achieve rectification ratios over 140, 10-fold improvement state art, nanofilms vanadium dioxide cubic boron nitride parallel-plane geometry at experimentally feasible gap sizes (\ensuremath{\sim}100 nm). Our rational design offers relative ease fabrication, flexible choice materials, robustness against deviations from optimal thicknesses. expect this work facilitate application diodes solid-state circuits energy-conversion devices.