Wednesday, May 07, 2008

Nanoclusters break superconductivity record

Al nanoclusters

Wow! Every now and again a paper on the arxiv leaps out at you and today there’s work from Indiana University in Bloomington that has got my eyeballs on stalks.

Get this: a team led by Martin Jarrold is claiming to have found evidence of superconductivity in aluminium nanoclusters at 200 K .

Yep, 200 K. The current world record for high temperature superconductivity is 138 K for a cuprate perovskite so that’s a massive jump.

The background to this is that two years ago Yuri Ovchinnikov at the Landau Institute for Theoretical Physics in Moscow and Vladimir Kresin at the Lawrence Berkeley Laboratory in California predicted that metal nanoclusters with exactly the right number of delocalised electrons (a few hundred or so) could become strong superconductors.

Now Jarrold and his buddies (Kresin and Ovchinnikov among them) have found the first evidence that this prediction is correct in individual aluminium nanoclusters containing 45 or 47 atoms . And they found it at 200 K.

A few caveats. Before a claim of superconductivity can be made, physicists require three unambiguous and repeatable lines of evidence. The first is obviously zero electrical resistance. The second is the Meisner effect in which the superconductor reflects an external magnetic field. And finally there must be evidence of a superconducting phase transition, such as a jump in the material’s heat capacity when superconductivity occurs.

What Jarrold’s team have measured is the last effect–a massive change in an individual nanocluster’s heat capacity at 200 K. That’s an important pillar of evidence which is consistent with superconductivity but it is not yet a slam dunk.

Jarrold and his team are simply time-stamping their efforts by publishing on the arxiv and you can bet your bottom dollar that they’re looking for other evidence right now.

Even with that proviso, this looks to be an important breakthrough which should be straightforward for other groups to replicate. The group’s work is not yet peer-reviewed. That’ll be an important step too.

Jarrold will be only too mindful that the field of high temperature superconductivity is littered with the corpses of physicists who have made premature claims.

But for the moment, sit back and admire. 200K…wow! That’s room temperature in Siberia at certain times of the year.

Ref: Evidence for High Tc Superconducting Transitions in Isolated Al45 and Al47 Nanoclusters

Earlier ref: Shell Structure and Strengthening of Superconducting Pair Correlation in Nanoclusters

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