Diamond is an electrical insulator well known for its exceptional hardness. It also conducts heat even more effectively than copper, and can withstand very high electric fields 1 . With these physical properties, diamond is attractive for electronic applications 2 , particularly when charge carriers are introduced (by chemical doping) into the system. Boron has one less electron than carbon and, because of its small atomic radius, boron is relatively easily incorporated into diamond 3 ; as boron acts as a charge acceptor, the resulting diamond is effectively hole-doped. Here we report the discovery of superconductivity in boron-doped diamond synthesized at high pressure (8-9 GPa) and temperature (2,500-2,800 K).Electrical resistivity, magnetic susceptibility, specific heat and field-dependent resistance measurements show that boron-doped diamond is a bulk, type-II superconductor below the superconducting transition temperature T c ≈4 K; superconductivity survives in a magnetic field up to H c2 (0)≥3.5 T. The discovery of superconductivity in diamond-structured carbon suggests that Si and Ge, which also form in the diamond structure, may similarly exhibit superconductivity under the appropriate conditions.With their potential for electronic applications as microchip substrates, high efficiency electron emitters, photodetectors and transistors, diamond and carrier-doped diamond have been studied extensively 3-6 . The extremely short covalent bonds of carbon atoms in diamond give diamond many of its desirable properties, but also constrain geometrically which dopants can be incorporated and their concentration. Because of its small atomic radius compared to other potential dopants, boron is readily incorporated into the dense (1.763×10 23 atoms cm −3 ) diamond lattice. Boron dopes holes into a shallow acceptor level close to the top of the valence band that is separated from the conduction band of diamond by E g ≈5.5 eV. Electrical transport studies of B-doped diamond, including high-pressure synthesized crystals and CVD (chemical vapour deposition) films, find that low boron concentrations n≈10 17 -10 19 cm −3 give a semiconducting conductivity with an activation energy of ~0.35 eV (refs 7-11). Increasing the concentration to 10 20 cm −3 gradually decreases the activation energy 9,10 , and for n≥10 20 cm −3 , the electrical conductivity acquires metallic-like behaviour near room temperature [8][9][10][11] that signals an insulator-metal transition near this concentration. A metallic-like conductivity has not been found, however, at low temperatures for any presently available B concentration, which has reached (2-3)×10 21 cm −3 (refs 8-11).We have studied B-doped diamond synthesized by reacting B 4 C and graphitic carbon at pressure, 8-9 GPa, and temperature, 2,500-2,800 K, for ~5 s. Under these conditions, polycrystalline diamond aggregates 1-2 mm in size formed at the interface between graphite and B 4 C. All the diamond aggregates had a metal-like lustre. Scanning electron microscopy (SEM) showed that the di...

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The heat capacity and thermal expansion of a high quality single crystal of MnSi were measured at ambient pressure at zero and high magnetic fields. The calculated magnetic entropy change in the temperature range 0-30 K is less than 0.1R, a low value that emphasizes the itinerant nature of magnetism in MnSi. A linear temperature term dominates the thermal expansion coefficient in the range 30-150 K, which correlates with an enhancement of the linear electronic term in the heat capacity. A surprising similarity among the variations of the heat capacity, thermal expansion coefficient and temperature derivative of the resistivity is observed through the phase transition in MnSi. Specific forms of the heat capacity, thermal expansion coefficient and temperature derivative of resistivity at the phase transition to a helical magnetic state near 29 K are interpreted as the combination of sharp first-order features and broad peaks or shallow valleys of as yet unknown origin. The appearance of these broad satellites probably hints at a frustrated magnetic state slightly above the transition temperature in MnSi.

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