Pressing Forward from Teeth to Superconductors

Found in teeth and bones as well as fertilizers and DNA, phosphorus is an insulator at room temperature. However, exerting a large amount of pressure on a stable specimen of phosphorus changes its crystalline structure, enabling it to superconduct at temperatures of around 10 K. Exerting even more pressure (2.5 Mbar, about 30,000 times greater than the pressure of clenching your teeth) can transform it again, to a body-centered-cubic (bcc) crystal structure (Akahama et al., Phys Rev B, 1 Feb 2000). Now, Sergey Ostanin of the University of Warwick in the UK and his colleagues have shown that bcc phosphorus crystals achieve superconductivity at higher temperatures, somewhere between 14-22 K. This is still much lower than the temperature of your mouth, even after an ice-cream headache. But such phosphorus superconductors might be very useful in spintronics. For example, they could be help in the construction of a superconducting spin switch, specifically one in which the phosphorus layer would lie in between a pair of ferromagnets, an arrangement that could alter its identity from superconductor to regular conductor (L. R. Tagirov, Phys. Rev. Lett, 6 September 1999). Furthermore, high pressures might not even be needed to make bcc phosphorus crystals: they could possibly be grown by depositing the atoms onto a substrate of iron, which itself organizes into a bcc structure. (Ostanin et al., Physical Review Letters, 22 August 2003)