Since the discovery 17 years ago of high-temperature superconductivity in such copper oxides as lanthanum strontium copper oxide, researchers have been taking a close look at related materials. If the copper oxides could surprise us in this way, they asked, what phenomena might lurk in other unexplored materials? Sodium cobalt oxide (Na x CoO2) has some answers.
First, this compound, which conducts like a conventional metal, performs much better than a metal as a thermoelectric material 1 —a material in which the flow of heat induces a flow of electricity, and vice versa. Next, a form of this transition-metal oxide with water molecules incorporated into its structure was recently found 2 to go superconducting below 5 K. Additional experimental and theoretical results now appear nearly daily on the e-print archive.
Most of the behavior seen so far suggests strong correlations between the electrons; it’s inconsistent with the conventional...
