Evidence of superconductivity at 9 degrees Fahrenheit, or 260 Kelvin, has been reported by scientists at Energy Conversion Devices Inc., a private research firm in Troy, Mich.
Unlike earlier claims by others, ECD's report is based not on a loss of electrical resistance at that temperature but on another phenomenon that is essential to a proof of superconductivity, the Meissner effect. This is the ability of a material to exclude, or repel, a magnetic field from another source. Only superconducting materials can do this.
The ECD material loses all electrical resistance at temperatures as high as 157 degrees below zero Fahrenheit, or 168 K, but parts of it display the Meissner effect at 260 K.
"This is what's got us going," said Stephen Hudgens, ECD's research director. "It says some volume within this material is going superconducting at 260."
Like most of the new ceramic materials that become superconducting at surprisingly high temperatures, ECD's superconductor contains several crystal structures compressed into one inhomogenenous chunk. Because manufacturing methods are still largely trial-and-error, some portions of the material may be superconducting while others are not.
Thus portions that become superconducting at 260 K will show the Meissner effect but if the electrical current must then pass through intervening normal conductors, the chunk as a whole will not be superconducting.