Figure 1

(a) Resistivity (open symbols and left ordinate) and Hall number (closed symbols and right ordinate) as functions of temperature for the same bulk, B-doped diamond sample. The inset shows the onset of a superconducting transition near $4.5\mathrm{K}$ below which the resistivity becomes immeasurably small at $3.4\mathrm{K}$. (b) ac susceptibility of the B-doped diamond and a comparably sized piece of Pb in a counterwound coil. The inset shows the onset of a diamagnetic response in B-doped diamond at $4\mathrm{K}$ that is followed below $2.3\mathrm{K}$ by a response comparable to that of Pb with $T_c=7.22\mathrm{K}$.Reuse & Permissions

Figure 2

Upper critical magnetic field as a function of temperature for bulk, B-doped diamond. The curves were constructed by taking the field-dependent temperatures at which $\rho \left(T\right)$, plotted in the inset, reached 90% (open circles) and 10% (filled circles) of its value just above the resistive onset. Representative data in the inset are, from right to left, for fields of 0, 1, 3, 5, 7, and $9\mathrm{T}$.Reuse & Permissions

Figure 3

Specific heat divided by temperature vs temperature for bulk, B-doped diamond. Two anomalies, corresponding closely in temperature to those found in ac susceptibility, confirm the bulk nature of superconductivity. The dashed line is an entropy-conserving construction, assuming an idealized transition at $4\mathrm{K}$. A linear fit of $C∕T$ vs $T^2$ for $T⩾4.5\mathrm{K}$, plotted in the inset, gives a sample-averaged electronic Sommerfeld coefficient $\gamma =0.113\mathrm{mJ}∕\mathrm{mol}\mathrm{C}∕{\mathrm{K}}^2$ and ${\Theta }_D=1440\mathrm{K}$.Reuse & Permissions