Why is the transition in resistance gradual at the Critical Temperature

[thanasis]

Hello. The measurement of electrical resistance as a function of the superconductor's temperature yields fundamental insights into its properties. The Critical Temperature, Critical Current Density, and the Critical Magnetic Field, can all be obtained through variations of a basic experiment.

I would like to ask you. Why is the transition in resistance gradual at the Critical Temperature (T0) on plot of resistance versus temperature ? ( see the attached picture ). Thank you !

 

[DuckAmuck]

The different regions in the superconductor aren't reaching critical temp at the same time.

 

[thanasis]

any help please ?

 

[DuckAmuck]

Like when you heat mashed potatoes in the microwave. They don't heat evenly right away. The same thing happens when you try to cool objects too.

 

[f95toli]

It also has to do with the quality of the superconducting film/material. The Tc of a superconductor depends on how uniform and pure the material is, meaning how steep the transition is will largely depend the quality: a "bad" film will always have a wide transition. This is one reason why the width of the transition is often used as a figure of merit when reporting on the quality of e.g. high-Tc materials.