Critical magnetic field and energy-gap anisotropy of zinc

The critical-magnetic-field curve of a single crystal of Zn has been determined from isothermal dc magnetization measurements over the temperature range from the superconducting transition temperature T₀=0.850 to 0.013 K. Values of the quantities T₀; H₀, the zero-temperature critical magnetic field; γ, the coefficient of the normal-state electronic specific heat; and ${\left(\frac{d{H}_c}{dT}\right)}_{T=T_0}$, the initial slope of the critical-magnetic-field curve, are given for pure Zn. These values were obtained from the single-crystal data which were corrected to include the effects of a slight amount (0.5 ppm) of Mn impurity. The shape of the critical-magnetic-field curve shows that Zn is a weak-coupling superconductor having a mean-squared energy-gap anisotropy parameter 〈a²〉 of 0.03. This value of 〈a²〉 is significantly lower than previoulsy believed.