How do impurities affect the critical temperature of superconductors?

[mojo0529]

I've search plenty of papers,but I still got no idea about this.Can anyone give me some clues?

Thanks in advance.

 

[fatra2]

Hi there,

Without being an expert in the field, superconductivity comes from the fact that electrons move more freely than in a conventional conductor. If you add some impurities in this material, you change the potential of electrons to move freely, by having variation in the lattice.

Like I said, this is really not my field. Cheers

 

[genneth]

Staying with conventional superconductors: non-magnetic impurities don't do much, and can in fact raise things like the critical field/current. Magnetic impurities tend to cause problems, and can destroy the superconductivity entirely.

 

[Minich]

For example: experiment for ordinary metals (1/2,... filled zone)

Superconductivity in amorphous and microcrystalline transition-metal alloys*
W. L. Johnson and S. J. Poon
In: Journal of Applied Physics. Vol. 46, No. 4. April 1975
W. M. Keck Laboratory of Engineering Materials. California Institute of Technology, Pasadena, California 91109 (Received 2 October 1974)
------------------------------------------------------------------------
... It is found that the transition temperature of an amorphous phase obtained by liquid quenching is always less than that of one of the related crystalline phases...

Since 1930 years Kikoin-Kitaygorodski-Chapnick empirical rule is known:
Almost 90-95% superconductors are hole-like (Hall coefficient just above Tc is positive)
See diagram

at http://physics.ucsd.edu/~jorge/bcs.html

See more about Kitaygorodski-Chapnick empirical rule at
"[URL theory of superconductivity: the world’s largest Madoff scheme?
J. E. Hirsch
Department of Physics, University of California, San Diego
La Jolla, CA 92093-0319[/URL]If impuruties make hole effective mass more in value (while Fermi momentum is constant), than Tc will be more in value (as a rule!).

But in ordinary metal impurities in some cases can change even the sign of effective mass! And in that case superconductivity may be destroyed completely.

Electron and hole conductivities compete in most metals, so it is hard to predict exactly Tc change.

In HTSC picture is more complex.