New superconductors discovered

The layers of carbon in graphite are loosely bound - you see them sliding onto your paper every time you use a pencil. These weakly bound layers in graphite allow 'guest' atoms to be inserted between the layers - a process called intercalation. These guest atoms change the electrical and mechanical properties of the graphite. Superconductivity in graphite was first found some 40 years ago, in a compound of graphite with potassium inserted between the layers (C8K). Superconductors are materials that become perfect conductors, losing their electrical resistance, when they are cooled below a 'superconducting transition temperature'. This characteristic temperature for C8K is 0.15K.

The doctorate work of Dr Tom Weller (UCL Physics and Astronomy), led to the preparation of the compound C6Ca formed by inserting calcium atoms between sheets of graphite. This compound when cooled to below 11.5K becomes a superconductor. Dr Weller's thesis work had also led to discovery that C6Yb superconducts at 6.5K. These new discoveries represent a leap in transition temperature and has stimulated a new debate concerning the superconducting properties in these graphite compounds. A paper detailing these discoveries has been published in October's launch issue of 'Nature Physics' and related articles appear in October's Physics World and on the Institute of Physics website.

Dr Weller said: "It's surprising that systems based on graphite have received little attention in this context. This discovery has far-reaching implications for applications such as carbon nanotubes."

• Links:
• UCL Condensed Matter and Material Physics Group
• Nature Physics
• Physics web