limitations of BCS theory?? (1 Viewer)

[mreditor16]

encountered this question in a NEAP paper. I have no idea what to write. suggestions people?

"Discuss the limitations of the BCS theory" (3 marks)

thanks in advance.

rep on offer for good answers*




* if BOS lets me ofc. i.e. unless i've given you rep recently, i'll rep you. if you have, still answer anyway

 

[Zeref]

it only explains superconductivity for type 1 superconductors therefore this theory is incomplete as it means there are other factors that come into play

 

[QZP]

BCS theory explains superconductivity using the concept of cooper pairs formed from the continual exchange of phonons between two electrons due to lattice distortions. However, the theory predicts that such cooper pairs can only form below a temperature of ~30K as too great of lattice vibrations causes too much scattering of the electrons to be able to form cooper pairs. Hence, BCS theory is limited as it only explains superconductivity in type 1 superconductors (pure metals) not type 2 superconductors (alloys, ceramics with higher Tc than 30K).

 

[mreditor16]

it only explains superconductivity for type 1 superconductors therefore this theory is incomplete as it means there are other factors that come into play

why does it only explain for type 1?

 

[mreditor16]

why does it only explain for type 1?

actually dw QZP explained it well!

 

[mreditor16]

*the BS theory. lol soz.

The main disadvantage is that the BCS Theory does not explain the superconductivity of Type II superconductors. It also fails to predict the effects of the actual superconductivity or which materials are superconducting. Instead, it simply provides an explanation for the 'events'. Furthermore (and I'm pretty sure this is beyond syllabus lol, I read ages ago from some textbook so don't take my word for it and do double check) it neglects electron-electron coulomb interaction. Its also a qualitative explanation.

Pretty sure it cannot be used to explain rotating superconductors too, but once again I'm honestly just relying on my memory from pre-trials cramming (and they didn't even ask on the BCS Theory ) and so do try and verify these LOL

Thanks!

You must spread some Reputation around before giving it to harrypotterfan again.

 

[hawkrider]

*looks at explanations*

*shudders*

 

[QZP]

*the BS theory. lol soz.

The main disadvantage is that the BCS Theory does not explain the superconductivity of Type II superconductors. It also fails to predict the effects of the actual superconductivity or which materials are superconducting. Instead, it simply provides an explanation for the 'events'. Furthermore (and I'm pretty sure this is beyond syllabus lol, I read ages ago from some textbook so don't take my word for it and do double check) it neglects electron-electron coulomb interaction. Its also a qualitative explanation.

Pretty sure it cannot be used to explain rotating superconductors too, but once again I'm honestly just relying on my memory from pre-trials cramming (and they didn't even ask on the BCS Theory ) and so do try and verify these LOL

I don't think this made sense at all (no offense)
1. It doesn't predict effects of superconductivity? From wiki: "BCS theory derived several important theoretical predictions... These have been confirmed in numerous experiments". An example is the Meissner effect which BCS theory correctly predicts.
2. It neglects electron-electron coulomb interaction? Not at all. The initial coulomb attraction between an electron and the positive cation allows for the phonon exchange (quantum particle of sound formed due to lattice distortions) between the first and second electron which negates their repulsion to form the cooper pair. Shortcut: Phonon exchanges overcome the electron-electron coulomb repulsion

And I don't think its a qualitative explanation. There's quite a lot of maths behind it if you look further into it but I can't explain that sorry (don't understand it)

 

[QZP]

yeah I did say to verify this LOL. Sorry, didn't articulate point 1 clearly: 1 basically meant lack of complete predictability power e.g. as to which materials will superconduct (we can only 'post-dict' it per se)– this can be verified by a variety of sources, a simple google search will confirm this. The second point about electron-electron coloumb interaction– something about how it fails to explain the inverse isotope effect or something, tbh I actually don't know too well, this was mainly a result of last-minute cramming for trials

But I found a source for it http://elk.sourceforge.net/CECAM/Massidda-superconductivity.pdf pg 26

Your last minute cramming involves reading university-level BCS theory? I don't think there's much point to quote limitations such as the "neglection of electron-electron coulomb repulsion" if there is no evidence to back it up and especially if HSC level knowledge and logic counteracts it (what I said above).

 

[Quantum College]

BSC only explains superconductivity for type one superconductors. Type I are usually pure metals like mercury with very very low critical temperatures.

It doesnt however explain superconductivity for type 2 superconductors which are metal alloys and ceramics that have much higher critical temperatures.