Built on Facts

You may have heard of the actinides, lanthanides, oxides, and various other -ide names from chemistry. Here’s another: pnictide. Rolls right off the tongue, no?

Well, you may be hearing more about them in the future.  In the race - now more like a marathon - to understand superconductivity, research has focused on the various copper oxides.  The most famous high-temperature superconductor is probably yttrium barium copper oxide, which broke the liquid nitrogen barrier for superconductivity in 1987.  The current state of the superconducting art is critical temperatures at standard pressure of about 135K.  This is much too hot to be explained by BCS theory, but of course it’s nowhere near the holy grail of room-temperature superconductivity.  We won’t know if that’s possible or not until someone either gets lucky and finds a material with that elusive property or until someone comes up with a decent theory of high-temperature superconductivity that either confirms or denies that such a thing is possible.  So far we’re not very close.

Dr. Paul Grant, writing in Nature, has an interesting article about a new experimental effort with new materials - the pnictides.  These are group 15 compounds, especially those involving iron, which had not yet thus far been adequately studied in terms of superconducting properties.  Right now these compounds have been demonstrated to have superconducting properties up to the 55K range.  But this isn’t particularly high in an absolute sense despite the fact that it’s vastly higher than previous records with these compounds.  In fact, there’s some reason to believe these might actually be on the bleeding edge of the range that standard BCS theory may be able to explain.  This potentially carries a great deal of interest, as the transition between regimes might finally shed some light on how high-temperature superconductivity works.  Or it might not.  There’s never guarantees.  As Dr. Grant said

Will T_c in the pnictides continue to go up, and perhaps double or triple as happened in 1987–88? I doubt it. We’ve now been on standby for several months, and to my mind the best hope is that the discovery of pnictide high-temperature superconductivity will help us understand better the physics of the cuprates. The iron age has yet to dawn.

Let’s hope it does.  Or if it doesn’t let’s hope we can figure out why.  From a pure science standpoint, both are equally fascinating possibilities.