Superconductivity of thin films. I. Mercury

Abstract

This paper describes the results of measurements of the superconductive properties of thin films of mercury prepared according to the method described in a previous publication (Appleyard and Bristow 1939). Previous workers on the superconductivity of thin films (Sizoo and Onnes 1925; Burton, Wilhelm and Misener 1934; Misener, Smith and Wilhelm 1935; Misener 1936; and Shalnikov 1938) have not been able to distinguish definitely between the effect of the finite size of their specimens (which is the feature primarily interesting from the theoretical point of view), and effects due to their uncertain structure which is often profoundly affected by the methods of preparation of the films. In particular they have not been able to show that the magnetic threshold value of their films approaches the value for the bulk metal when the thickness of the films is sufficiently increased except at very great thicknesses. Shalnikov (1938), for example, has performed a series of experiments on superconducting thin films of lead and tin. But his thickest films seem to have had a critical field 2-3 times in excess of the bulk metal, and his results seem not to have been very reproducible (Shoenberg 1938). Pontius (1937) also obtained definite indications of a size effect with fine wires of very pure lead, but the difference in behaviour from that of the bulk metal was small. Results from wires are certainly reliable for the dimensions obtainable, but the difficulty of drawing a wire thinner than about 10 -4 cm. sets a limit to the scope of the method.