Zur Änderung der übergangstemperatur verschiedener Supraleiter durch Elektronenentzug

Abstract

The growing of oxid layers on pure metal films at low temperatures may be explained by acceptor levels at the oxid-oxygen interface. These surface states produce an electrical field of high strength by extracting about 10¹⁵ electrons per cm² out of the metal film. As had been shown in earlier experiments, this capturing process shifts the superconducting transition temperature to higher values for the 3-valent metals Al, In and Tl and to lower values for the 4-valent metals Sn and Pb. Extended studies on Tl show that this change in transition temperature is proportional to the relative decrease of the electron density in the metal film. The constant of proportionality has the valuek _Tl=−4.4 deg. With reasonable assumptions, this constant could be determined for Sn too:k _Sn=7.9 deg. These values agree quantitatively with the results ofGlover andSherill who investigated the charge effect on superconductors by a condenser method. They also fit the data calculated byGinsberg from experimental results on superconducting compounds with his extension of the theory ofMarkowitz andKadanoff.