High Transition-Temperature Superconducting

Lee S, Myers WR, Grossman HL, Cho HM, Chemla YR, Clarke J (2002) Magnetic gradiometer based on a high-transition temperature superconducting quantum interference device for improved sensitivity of a biosensor. Appl Phys Lett 81 3094-3096... 

In early 1987, the composition and structure of the La-Ba-Cu -O superconductor was still unknown to the general public in the United States. By March of that year certain facts became known from Japanese publications. But at this point in time, a newer, higher Tc (> 90 K) material was announced. This new copper oxide superconductor was quite easy to prepare and, in addition to interested physicists, these new materials could be synthesized by ceramists, chemists, metallurgists, material scientists, or anyone with a knowledge of a chemical approach to solid-state materials. Even high school students developed simple methods for the synthesis of these compounds. The "high" transition temperature and the possible use of liquid nitrogen made research in superconductivity accessible to most scientists and laboratories. The media also capitalized on this worthy news report and published it in newspapers and also presented it on television as a news item. 

Lee, P.J. Engineering Superconductivity, Wiley-IEEE Press, New York, NY. 2001. Little, W.A. Experimental Constraints on Theories of High-Transition Temperature Superconductors, 5 Science, 1390 (December 9, 1988). 

Ever since this breakthrough, C60 has been intensively studied and has shown its rich bonding characteristics in various environments, from van der Waals cohesion to ionic and metallic cohesions, and even to the extent of covalent bonding, together also with its rich electronic properties including high transition-temperature (Tc) superconductivity in alkali-doped C60 fullerides. This article reviews the first-principles quantum-mechanical studies of these electronic and bonding properties of C60. 

The following summary of the essentials of the phenomenon and theory of superconductivity serves to introduce terminology and permits the high transition temperatures (Tc) superconductors (HTSs) to be seen in a historical... 

The carbon atoms are in a nearly sp hybridized state which relates these compounds strongly to the conjugated polymers and guarantees the same colorful vibrational spectroscopy as described in the above subsections. Also, the fullerenes can be doped to a metallic state which in some cases even goes superconducting with a rather high transition temperature (Rosseinsky et al., 1991). The state of the art in fullerene research up to 1993 is well described in (Dresselhaus et al., 1993). 

But while the BCS theory applied to low-temperature superconductivity, Little s model, after detailed calculations were carried out, had an enormously high transition temperature—typically around 2,000° K. 

CrjSi, which is a candidate phase for high-temperature applications, and VjSi, which is superconducting at low temperatures with a comparatively high transition temperature, both crystallize with the topologically close-packed cubic, A15 structure and have been discussed in Secs. 7.7 and 7.2, respectively. 

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