Interband-Pairing-Boosted Supercurrent Diode Effect in Multiband Superconductors

We unveil a mechanism that enables a robust supercurrent diode effect in Josephson junctions based on multiband superconductors. We predict that interband pairing can significantly amplifies this effect, even under weak spin-orbit coupling while intraband pairing alone would render it negligible. To illustrate this, we examine monolayer FeSe/STO, a system where recent experiments suggest interband pairing in either a nodeless $d$-wave or $\eta$ pairing state. Using experimentally derived parameters, we predict that FeSe/STO can serve as a high-temperature platform for realizing a substantial supercurrent diode effect, with efficiencies reaching up to $30\%$ for $d$-wave pairing and $12\%$ for $\eta$ pairing. These results demonstrate that measuring the supercurrent diode effect can provides a powerful probe of the pairing symmetry in monolayer FeSe/STO, offering critical insights into its superconducting state.