Electrical behavior of Te, Se, and S at very high pressures and low temperatures: Superconduction transitions

At sufficiently high pressures Te, Se, and S transform to metallic or semimetallic forms. Earlier work showed the metallic forms of Te and Se to be superconductors, and very recent Soviet reports indicate that high-pressure metallic S becomes superconducting. The work reported in this article covers more refined measurements of the resistivities and temperature coefficients of these elements in metallic form as related to pressure, and the resistance behavior from room temperature down to 2.7 K. Metallic Te and Se prove to be good superconductors. In our experiments semimetallic S shows a minimum resistance in the 150-100-K zone, and a reproducible and consistent "jog" in the $R(T)$ curve at about 10 K. This resistance behavior of sulfur over the range 12 to 300 K can be formulated as a series combination of a metal-like component and a semiconductinglike component, as might be expected in a partially converted specimen. In such a case a possible explanation of the downward jog in the 10-K region could be a superconduction transition in the metallic component. However the magnitude of the observed jog is actually far too small to be accounted for by such a model. It may be that the unusual resistance and temperature behavior is the result of complicated electronic properties of a high-density, complex, linear sulfur structure which involves electron hopping from one linear molecule to another. Some fits to a Mott T^-1/4-type model and an Anderson T^-1 type are tried but appear to be only partially successful.