Ideal superheating and supercooling limits in superconducting In and diluteInBi alloys

We have observed the ideal superheating and supercooling fields in 18-{μ}m single spheres of In and InBi (0.19, 0.395, and 0.60 at.%). Extrapolation of HscHc to $t=1$ gives κ(t=1)=0.061, 0.155, 0.240, and 0.349, respectively, to an accuracy of 2%. The values of HₛₕHc at $t=1$ are 3.39, 2.44, 2.08, and 1.85, respectively, to 2% accuracy. These values are higher by 0%, 14%, 21%, and 30% than those given by the asymptotical expression Hₛₕ=Hc(κ√2)1/2 which is valid as κ→0. This is in fair agreement with one-dimensional Ginzburg-Landau theory for finite κ. Close to Tc, the hysteresis shrinks markedly as the tricritical point is approached. In the InBi (0.60-at.%) sample, Hsc exceeded the demagnetizing field HD, thus permitting observation of the intermediate state, the demagnetizing field HD, and Hc. HD shows a marked size effect, Hc almost none. In this sphere, the intermediate state can be made to superheat far beyond Hc. We interpret this as ideal superheating in the equatorial region, while a frozen-in normal domain is located along the polar axis.