Modeling Iridium-Based Trilayer and Bilayer Transition-Edge Sensors

We report a model that can be used to calculate superconducting transition temperature of a transition-edge sensor (TES), which is either a normal metal–superconductor–normal metal trilayer or a normal metal–superconductor bilayer. The model allows the $T_{C}$ estimation of a trilayer when the normal metals at the bottom and at the top are different. Furthermore, the model includes the spin flip time of the normal metals. We use the $T_{C}$ calculations from this model for selected Ir-based trilayers and bilayers to help understand potential designs of low $T_{C}$ TESs. A Au/Ir/Au trilayer can have a low $T_{C}$ because the superconducting order parameter is reduced with normal metals at both sides. On the other hand, an Ir/Pt bilayer can have a low $T_{C}$ because the much larger electron density of states of Pt reduces the superconducting order parameter more effectively. Moreover, the spin flip scattering of paramagnetic Pt also contributes to the $T_{C}$ reduction.