# What effect would one expect if the Critical Temperature is

Tags:
1. Dec 18, 2015

### thanasis

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. What effect would one expect if the Critical Temperature is measured with the device placed inside a functioning electromagnet?

2. Dec 18, 2015

### f95toli

It will depend on a number of factors and also how you measure Tc (resistive or inductive measurement).
Also, are you thinking of a type I or type II superconductor?

3. Dec 18, 2015

### thanasis

both of them. Type one and two. Resistive measurement.

4. Dec 18, 2015

### f95toli

In type II it gets complicated since it will depend on lots of factors since the width of the transitions can depend on if and where vortices are formed (in a narrow strip you can get some DC resistance because of flux, even for quite small fields): : the strength of the field relative to Bc1 and Bc2, geometry etc. Experimentally this means that the width/shape of the transition canl be field dependent, up to the point where you exceed Bc2 and the whole thing goes normal (although when that happens will also depend on geometry)..

Type I is easier to understand since it will basically exclude the field until you exceed Bc, although in a real experiment .this will also depend a bit on geometry (both because there can be local variations in Tc, and because of flux focusing). However, for bulk it is fairly easy to understand (although most resistive measurements will be done on thin films where the aforementioned factors will come into play).

5. Dec 18, 2015

### thanasis

so what effect would one expect if the Critical Temperature is measured with the device placed inside a functioning electromagnet?

6. Dec 18, 2015

### f95toli

I thought I explained that above. It will depend on several factors, so there is no simple answer to that question.
It is only "easy" for a bulk type I superconductor, but the details of what you would actually measure with a resistive measurement can still get quite messy.

There are even some exotic superconductors (quasi-2D) where the critical temperature goes up if you apply a magnetic field.

Also, what do you mean by "functioning electromagnet"? How the field is generated is irrelevant; only the strength (and for some geometries the direction) of the magnetic field is relevant.