Boron-doped diamond is material promising for various applications in biology and electrochemistry showing remarkable transport properties, superconductivity including. Understanding of the mechanism of electron transport in this material is an interesting physical problem, the solution of which is important both in applications and as a guide for the study of other superconductors. In nanocrystalline diamond, containing ca 1 at % of boron we investigated electrical conductivity in the temperature range between 1.2 and 400 K. Material showed a transition into the superconducting state at about 1.7 K. Analysis of the temperature dependence of resistivity indicates that the conductivity is controlled by a disintegration of so-called weakly localized electron or hole orbits. This finding led to a proposal of a model of unconventional superconductivity, according to which pairing of weakly localized holes is responsible for the transition to the superconducting state, attractive interaction being controlled by a spin-flip mechanism.
The temperature dependence of resistivity of boron-doped nanocrystalline diamond (B−NCD). Under a temperature of approximately 3 K a steep decrease in resistance is observed, which corresponds to the transition to the superconducting state. The behaviour of the temperature dependence above the transition (weak increase of resistance with decreasing temperature) differs significantly from the curves observed in common superconductors, such as lead (red curve in the insert). Just a different shape of the temperature dependence of resistivity above the superconducting transition is a significant indicator of the fact that the superconductivity in boron-doped diamond is controlled by an unconventional mechanism.
Reference
J. J. Mareš, P. Hubík, J. Krištofik, and M. Nesládek
Selected topics related to the transport and superconductivity in boron-doped diamond
Science and Technology of Advanced Materials 9 (2008) 044101 (6pp).
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