Martin Jarrold,Indiana University in Bloomington, is claiming to have found evidence of superconductivity in aluminium nanoclusters at 200 K. 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. Hopefully this leads to other materials that work at high temperature and which can be incorporated into products and applications.
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.
In other superconducting news: Researchers found that atomic areas where electrons were strongly repulsive when at non-superconducting high temperatures were where there was the strongest connections when superconducting at low temperatures. [Important for developing better theories and hopefully guiding experimentation.]
They found that atomic locations of the sample in which electrons show signs of stronger repulsion for each other — at very high temperature — formed the strongest bonded pairs of electrons at low temperatures. This observation runs contrary to the behavior of electrons in low-temperature superconducting materials, in which electron-electron repulsion is not conducive to electron pairing up and superconductivity.
They found that when the samples were heated up to very high temperatures at which electrons no longer paired up, the electrons that had been superconducting at colder temperatures exhibited unique quantum properties at warmer temperatures indicating they possessed extremely strong repulsive forces.