I've been following a literature search for the last few days that's led to a very interesting point. Superconducting tin has different quench points, (via magnetic field), depending on the orientation of the direction of current flow in the sample and the direction of the applied external magnetic field. My next job will be to determine if Pb has the same qualities, and if so what that means for the experiment.
Pb was chosen as the sample for our experiment because of the relatively low magnetic field strengths at which it can be quenched. It was mentioned by Hirsch in one of his articles predicting Bremsstrahlung radiation from quenched superconductors that the super conductor should be quenched 'quickly'. It's unclear at the moment what effect this squirmy quality of supercurrents vs. magnetic field orientation will have.
Flow of the Literature Search:
And now, just a few notes on how I arrived at the Shubnikov article. Hirsch who originated the theory that predicted the Bremsstrahlung we're trying to detect wrote an article that mentioned the similarities between superconductors and superfluids. In that article, he references Mendelssohn who thought that superconductors might behave in the same way as liquid helium via what he termed zero point pressure. Upon searching for more articles by Mendelssohn, I came up with an article he wrote with Keeley  where there experimental evidence of frozen in fluxes sounded very much like type II superconductor behavior with pinned fluxes. That led to a perusal of Abrikosov's Nobel prize lecture on type II superconductors which ultimately led to Shubnikov's article. Abrikosov credits Shubnikov's data as helping to confirm his theories on type II superconductors.
Mendelssohn in addition to his superconductor work in the 1930's also wrote a book on the Great Pyramids in the 1970's .
Shubnikov was exectued by the KGB in 1936, (the same year he published the paper I reference), for allegedly being involved in an 'anti-Soviet strike'.
1. Shubnikov's article in which the change in quench field vs current direction is observed
2. Peierls article in which the intermediate state is defined:
3. Keeley and Mendelssohn experimenting with frozen in flux
5. Abrikosov's Nobel prize lecture on type II superconductors
6. Mendelssohn's book on pyramids
Picture of the Day: