Superconductivity inβ-Phase Gallium

Abstract

An experimental study of the superconducting properties of small single spheres of $\beta$-gallium has been made. Some spheres exhibited little superheating and went into the intermediate state so that $H_c\mathrm{}\left(T\right)\mathrm{}$ could be determined, giving $H_0=538\mathrm{}\pm 5$ Oe. The deviation of $H_c\mathrm{}\left(T\right)\mathrm{}$ from a parabolic temperature dependence is positive, indicative of strong-coupling superconductivity. $T_c$ is 5.90±0.03 K. For temperatures close to $T_c$, ideal superheating and supercooling is observed in the best spheres, allowing the determination of the Ginzburg-Landau parameter $\kappa =0.141\mathrm{}\pm 0.002$. The variation with temperature of the signal difference between the superconductive and normal states determines the penetration depth of the magnetic field, giving ${\delta }_0=880\mathrm{}\pm 100$ Å. When the finite penetration depth is taken into account, agreement is obtained between the extrapolated values of ${\kappa }_{\mathrm{sc}}\mathrm{}\left(T\right)\mathrm{}$ and ${\kappa }_{\mathrm{sh}}\mathrm{}\left(T\right)\mathrm{}$ at $T_c$.