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........ published in NEWSLETTER # 62

by Professor M. Ausloos, University, Liege (Belgium)

The last decade has brought substantial progress in the physics of superconductivity due to the discovery, and subsequent numerous investigations, of high critical temperature superconductors (HTcS). Such new materials have opened up promising possibilities of various applications in advanced technologies. The scientific problem of studying HTcS is one of the most prominent ones in solid state science, with thousands of laboratories involved. Nevertheless the nature of HTcS impedes the expected technological progress necessary for practical applications. This is due to the specific properties of HTcS, i.e. an extremely short coherence length, a high value of the critical temperature, a low density of charge carriers, and the strong anisotropy determining the effective dimensionality of charge motion.

The understanding of the role of "fluctuations" is also necessary for future technological applications of these materials since the fluctuations may destroy the superconducting state. The essential role of perturbations should be thus understood for advancing the choice of optimal working conditions and best regimes of devices. All this has led to a world-wide effort in studying "fluctuations" in HTcS.

The possibility of extracting information on the charge spectrum anisotropy, on the order parameter symmetry, on the various scattering mechanisms, on the response to an external magnetic field, should directly result from the analysis of fluctuation contributions per se. Moreover, from a fundamental point of view, the magnitude and range of fluctuations effects in HTcS, the ballistic character of the charge motion and the spectrum anisotropy also generate not only qualitatively but also quantitatively new phenomena not previously known in other systems. Therefore, the complexity of the theoretical analysis, the need for excellent experimental work, and finally the confrontation of results, together with the existence of hundreds of articles, but also the total absence of a review article in the past 20 years led to a NATO Workshop in Trieste in August 1996 and to a book edited by M. Ausloos and A.A. Varlamov.
The book (NATO ASI SERIES 3-32) covers:

1. Superconducting fluctuations in the vicinity of the Ginzburg- Landau critical transition - the effect of fluctuations on static properties, including the c-axis density of states, - the effect of fluctuations on electrical and thermal transport, properties in the ab-plane and along the c-axis, - the effect of magnetic field on fluctuation phenomena in specifically layered compounds.

2. Specific fluctuations of the vortex lattice in the (B, T)-plane - the vortex state in HTcS is much more complex in comparison to conventional superconductors.

In conclusion, this volume containing review, introductory and advanced level topics should become a landmark in the field. In fact, the mechanisms of superconductivity in HTcS, the order parameter symmetry and the material response in a magnetic field are very hot research topics these days. The ARW proceedings will likely serve as a major step for the community in resolving that dilemma.
Reference books: 3-32, B7, B100, B155, B246, E181, E209, E251, E263, F59

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