Le Aug 3, 2012 à 8:29 AM, David Roberson <dlrober...@aol.com> a écrit :
> The fact that a certain temperature makes a difference tends to suggest the > rearrangement of grains of the material which is a characteristic of magnetic > behavior. Nickel is particularly responsive to magnetic fields. I've been reading a number of interesting articles and papers touching on high temperature superconductivity. Some interesting details: there are different "orders" that appear under different conditions; a ferromagnetic order, a metallic order, a charge wave order, a superconducting order, and so on. The temperature and external magnetic fields are important parameters in determining which orders prevail at a given time. When superconductivity does come about, it does so gradually, in localized domains, which grow larger as the conditions become more favorable until the entire surface or bulk is superconducting. > There are different types of superconductors; there are ones in which the effect appears in the bulk, in all directions, as well as ones in which it appears in one or two dimensions of the crystal. And then there are so-called topological insulators, where the effect appears at the interface between two insulators. Physical strain is an important variable, and the strain on the lattice produced by the interposition of hydrogen can cause sufficient modification of the crystal to cause an order that was previously suppressed, such as the magnetic order, to appear, thereby bringing about superconductivity. I'm wondering at this point whether superconductivity itself is pertinent. From what I have read, no room-temperature superconductivity has been discovered yet, let alone superconductivity at 300 or 600 C. But (1) the possibility of a surface effect related to plasmon modes, (2) the appearance of the effect in small domains and (3) the relevance of the gradual onset of the magnetic order are all interesting leads. Eric
