Very large thermal rectification in ferromagnetic insulator-based superconducting tunnel junctions

We investigate electronic thermal rectification in ferromagnetic insulator-based superconducting tunnel junctions. Ferromagnetic insulators coupled to superconductors are known to induce sizable spin splitting in the superconducting density of states and also lead to efficient spin filtering if used as tunnel barriers. The combination of spin splitting and spin filtering is shown to yield a substantial amount of self-amplification of the electronic heat diode effect due to breaking of the electron-hole symmetry in the system, which is added to the thermal asymmetry of the junction. Large spin splitting and large spin polarization (⁠$≳90%$⁠) can potentially lead to thermal rectification efficiencies exceeding $∼5×104%$ for realistic parameters in a suitable temperature range, thereby outperforming up to a factor of $∼250$⁠, the heat diode effect achievable with conventional superconducting tunnel junctions. These results are relevant for improved control of heat currents in innovative phase-coherent caloritronic nanodevices and for enhanced thermal management of quantum circuits at the nanoscale.