Mapping of the resistance of a superconducting transition edge sensor as a function of temperature, current, and applied magnetic field

We have measured the resistance R ( T , I , _{B ext} ) of a superconducting transition edge sensor over the entire transition region on a fine scale, producing a four-dimensional map of the resistance surface. The dimensionless temperature and current sensitivities ( α ≡ ∂ log R / ∂ log T _{| I} and β ≡ ∂ log R / ∂ log I _{| T} ) of the TES resistance have been determined at each point. α and β are closely related to the sensor performance, but show a great deal of complex, large amplitude fine structure over large portions of the surface that is sensitive to the applied magnetic field. We discuss the relation of this structure to the presence of Josephson "weak link" fringes.