Superconductivity in β-phase gallium

An experimental study of the superconducting properties of small single spheres of β-gallium has been made. Some spheres exhibited little superheating and went into the intermediate state so that Hc(T) could be determined, giving H0=538±5 Oe. The deviation of Hc(T) from a parabolic temperature dependence is positive, indicative of strong-coupling superconductivity. Tc is 5.90±0.03 K. For temperatures close to Tc, ideal superheating and supercooling is observed in the best spheres, allowing the determination of the Ginzburg-Landau parameter κ=0.141±0.002. The variation with temperature of the signal difference between the superconductive and normal states determines the penetration depth of the magnetic field, giving δ0=880±100. When the finite penetration depth is taken into account, agreement is obtained between the extrapolated values of κsc(T) and κsh(T) at Tc. © 1973 The American Physical Society.