Mechanism underlying the superfluid-stiffness–transition-temperature crossover

Determine the microscopic origins of the weak dependence of superconducting transition temperature on superfluid stiffness at large stiffness, the crossover between weak and rapid dependence, and the rapid suppression of transition temperature at low stiffness in FeTe thin films.

Background

The experiments find that the local transition temperature depends only weakly on the zero-temperature superfluid stiffness at large stiffness, but is rapidly suppressed when the stiffness approaches the scale of the transition temperature. The authors discuss phase fluctuations, disorder-induced pair breaking, and inhomogeneity as possible mechanisms.

The lower-transition-temperature samples exhibit pronounced spatial variations, so homogeneous theories of disorder-induced pair breaking may be insufficient. A quantitative microscopic account of the observed crossover and its relation to interstitial-Fe disorder and phase fluctuations remains unresolved.