Results are presented of the Kapitza resistance of lead specimens between I and 2 K. The specimens underwent surface treatments which included annealing, electropolishing, argon ion bombardment, and finally surface preparation by guillotining under liquid helium. The difference in Kapitza resistance between normal and superconducting states is seen to be compatible with the presence of a bulk thermal resistance due to mechanical strain which is operative in the superconducting state only. A preliminary result on a Pb--20% at In alloy is also given.
Some experimental investigations of the Kapitza resistance of lead J. D. N. Cheeke
There have been a large number of measurements of the Kapitza conductance of lead during the last ten years.l-9 This is partly due to the fact that the Kapitza conductance of all solids with He 4 is still an unresolved problem; a general review of the subject was recently given by Pollack.t 0 However interest in lead was mainly stimulated by Challis' observation 1 that at the superconducting-tonormal state transition in lead at 1"3 K, hlv/hs ~ 3, where hi = 1/R~ = Q/AAT in W cm -2 IC l and N, S refer to normal and superconducting states respectively. This observation was taken as evidence of the participation of the conduction electrons in the heat transfer process in the normal state, as predicted by Little ~ J who used standard perturbation techniques to calculate the interaction between the surface wave set up in the solid by the incident liquid phonons and the conduction electrons of a free electron metal)2 This calculated value of the electronic conductance (h ~t) was however orders of magnitude less than the effect observed by Challis.
Challis further observed 2 that hN/hs and hN, hs decreased as a function of the time for which the specimen was kept at room temperature. This he attributed to progressive oxidation of the surface. The magnitude of the field effects found in 1,2 was confirmed by Gittleman and Bozowski 3 and by Barnes and Dillinger, 4 the former showing that hu/hs was only of the order of a few % for Sn and In. Further results on lead were reported by Kuang Wey-Yen. s In a series of experiments in which the superconducting lead surfaces were scraped under liquid helium II, he showed directly the important role of surface strain by reducing the conductance of a strained surface by a factor of ten compared to that of the annealed surface.