Superconducting diamond turns up in Russia
Mar 31, 2004
Physicists at the Russian Academy of Sciences are claiming to have created a form of diamond that superconducts. Vladimir Sidorov and colleagues say that their material, which they made by doping carbon with boron at high temperatures and pressures, exhibits bulk superconductivity below around 4 kelvin and remains a superconductor in strong magnetic fields (E A Ekimov et al. 2004 Nature 428 542).This is the first time that boron-doped diamond -- which is normally a semiconductor -- has shown superconducting behaviour.
Diamond is usually an electrical insulator and well known for being exceptionally hard. It also conducts heat well and can withstand strong electric fields. These properties make it attractive for electronics applications -- especially when doped with charge carriers, such as boron. By reacting boron carbide (B4C) with graphitic carbon at around 8 gigapascals and 2500 kelvin for a few seconds, Sidorov and co-workers were able to create boron-doped diamond . Nuclear magnetic resonance and mass spectrometry revealed that the diamond contained between 2 and 3% boron.
By measuring the electrical resistivity and magnetic susceptibility of the diamond, the Russian physicists calculate that it has a superconducting transition temperature (Tc) of about 4 kelvin. This is the temperature at which the resistance of a superconductor drops to zero. Moreover, the material remains superconducting in magnetic fields of more than 3.5 tesla.
Sidorov and co-workers say their that data are consistent with the Bardeen-Cooper-Schrieffer theory of superconductivity. This theory states that interactions between electrons and vibrations of the crystal lattice -- known as phonons -- allow electrons to overcome their mutual electrostatic repulsion and bind together to form pairs, leading to superconductivity.
Proving that such samples are superconducting is far from easy and the findings are likely to fuel debate in the diamond community. In particular, the observed behaviour could simply be due to foreign substances percolating in the bulk of the material. Sidorov’s group will now need to conclusively prove that its material is superconducting. It also hopes to unearth superconductivity in other group-IV elements with the diamond structure, such as silicon and germanium.
About the author
Belle Dumé is Science Writer at PhysicsWeb