β Scribed by W.J. De Haas; O.A. Guinau
No coin nor oath required. For personal study only.
The transition from the s u p r a c o n d u c t i v e state to the non-supraconductive state of monocrystalline spheres of tin has been studied. First the t e m p e r a t u r e was held constant and a magnetic field applied, the intensity of which was gradually raised until s u p r a c o n d u c t i v i t y was entirely disturbed. The field was determined A ) on the pole of the sphere, B) on its equator, C) in a space between two hemispheres, D) in the space round the sphere, E) in a canal, parallel to the lines of force, F) in a canal perpendicular to them. The results can be described by ascribing to the sphere an a p p a r e n t permeability, equal to zero as long as the applied fieldstrength is lower t h a n ~ of the field which disturbs s u p r a c o n d u c t i v i t y entirely. This permeability zero must however be caused by a single current on the surface of the sphere and not by areal perfect diamagnetism of the material. The permeability increase s linearly with the difference of the applied fieldstrength and ~ of the critical fieldstrength, until it reaches the value one, when the applied fieldstrength reaches the critical one. F r o m thereon s u p r a c o n d u c t i v i t y is entirely disturbed and the " permeability remains equal to one. The field penetrates at ~ of the critical fieldstrength t h r o u g h o u t the sphere at once. A possible difference between the critical fieldstrengths, as deduced from these experiments and those, deduced from the measurements of the resistance of monocrystalline wires in a longitudinal field is discussed.
A second t y p e of transition has been studied. Here the external field remains constant and the t e m p e r a t u r e is raised. Until the critical fieldstrength is lowered so far t h a t the external field becomes ~ of it, neither on the pole nor in the space between the two hemispheres a field is found. The field on the e q u a t o r remains equal in t h a t i n t e r v a l to ~ the applied field. When the applied field is higher than ~ of the critical field, the field on the pole and in the space between the hemispheres increases, t h a t on the e q u a t o r decreases and this is always equal to the critical value at the given t e m p e r a t u r e . The sphere behaves first as a body with a permeability equal to zero, which increases linearly to one in the interval of transition.
π SIMILAR VOLUMES
Calorimetric experiments were performed on thallium in connection with the transition, in a constant magnetic field, from the supraconductive to the non-supraconductive state. A definite latent heat was measured. The values found were compared with thermodynamic theory. From the experimental data a
A discussion is given of the theory of the transition of a sphere from the superconducting to the normal state and it is shown that the fact, that during the beginning of the transition process the induction is distributed homogeneously can only be accounted for by assuming the existence of persisti