# What can be seen if taking a snap shot @ 4.21K? Superconductivity

1. Apr 12, 2014

### paulzhen

In the above picture it is clear that the transition from normal to superconducting states is not infinitesimally sharp, it drops from around 4.22K ~ end at 4.20K. I have two questions for this:

1) I wondering, what can be seen if taking a snap shot in the middle, say @ 4.21K? Would I see cooper pairs and free electrons mixed?

2) But as I know, cooper pairs would not "mix" with free electrons, because the exist of free electrons will disturb or say, break the condensed states of cooper pairs, it means either 100% cooper pairs or 100% free electrons in the conductor. Is my understanding right?

THANKS A LOT FOR HELPING!!

2. Apr 12, 2014

### ZapperZ

Staff Emeritus
The transition, in principle, is "sharp" because this is similar to a phase transition. However, in practice, we don't see it because (i) the uniformity and purity of the sample (ii) the resolution of the instrument, etc.

But secondly, you need to realize that even in a completely superconducting state, there are both paired and unpaired electrons! In other words, there are electrons in the supercurrent, and there are normal electrons! Not all the electrons condense into the supercurrent.

Zz.

3. Apr 12, 2014

### paulzhen

Dear Zz,

So the "transition range" from 4.22k to 4.20k shown in this diagram is only due to the issues such as impurities or instrument? But I believe it still require "a tiny period of time" to complete forming cooper pairs, right?

I am looking for some "proofs" for the exist of this "tiny period of time", any advice for me? Thanks!

4. Apr 12, 2014

### ZapperZ

Staff Emeritus
I have no idea what you mean by "a tiny period of time". That measurement as nothing to do with "time". I can vary the temperature as fast and as slow as I want to. So what does time have anything to do with this?

Furthermore, it appears that you no longer care about your original question, which is the presence of both cooper paired electrons and normal state electrons, even in the superconducting state.

Zz.

5. Apr 12, 2014

### paulzhen

Dear Zz,

Sorry I have thought for a long time how to make myself clear, but I failed obviously.

I just want to keep my post short hence did not tell the background of why I asking this question, because I think you would not interested in. You have answered my original question in your first reply, I took it and not going to ask more regarding to that.

What I really care about is:
I reckon there would be some evidence can be "seen" in this phase transition. Just like water transforming to ice, you can see ice and water mix in the middle of transition, and this transition took time. So I asking myself is there possible to "see" or more practically speaking, find some "proofs" for this period of superconducting transition. Since this is a "phase transition", I cannot imagine how anything "transform" to other things without any "intermediate state".

I thought the graph above is an evidence for this "intermediate state", but I believe I was wrong, so I am asking for another advices, hopefully I have made myself a bit more clear now.

Last edited: Apr 12, 2014
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