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"Superconductivity: approaching the century jubilee"

Relatore: Andrei Varlamov- INFM and Università di Tor Vergata, Dipartimento di Ingegneria Meccanica

Aula Newton
18 Maggio 2011 ore 16.00

Probably almost all have heard of superconductivity. This phenomenon consists of the abrupt disappearance of electrical resistance of some pure metals and alloys at low temperatures. ``Low temperatures'' meaning the range of 10—20 K, that is 10--20 degrees above the absolute zero (-273.15 C). Throughout the last century physicists and chemists in many laboratories all over the world were looking for compounds which become superconducting at high enough temperatures to be cooled, for instance, by comparatively cheap and widely available liquid nitrogen. So understand that the discovery of high-temperature superconductors in 1986, whose resistance becomes zero at temperatures above 100 K, was met as the greatest event in physics of recent years. Really, the practical significance of this discovery can be compared to that of magnetic induction at the beginning of the 19th century. It ranks with the discovery of uranium fission, the invention of the laser, and the discovery of the unusual properties of semiconductors in the 20th century. The main stumbling block in application of the available high-temperature superconductors is their poor technological properties: they are extremely brittle and do not stand rolling which is an essential element of mechanical treatment of metals. Nevertheless, several brands of high-temperature superconducting cables that are kilometers long are already on the market. A number of experimental underground transmission lines made of such cables are in operation now in France and the USA. The first electric motors and generators based on high-temperature superconductors are under testing. There is no doubt that the field of applications of these materials will expand and new, more-practical high-temperature superconductors will appear. Many global projects of the past are put back on the agenda because of the advent of high-temperature superconductivity. For example, at present 20--30% of all produced electrical energy is wasted in power transmission lines. Using high-temperature superconductors in energy transmission could eliminate these losses. All projects involving thermonuclear synthesis need giant superconductive magnets that keep high-temperature plasma away from the walls of the chamber. Streams, if not rivers, of liquid helium are necessary to maintain the superconducting state. The helium would be replaced by nitrogen at a tremendous cost saving. Gigantic superconducting coils would serve as accumulators of electrical power, which would share the load during peak periods. Supersensitive equipment for making magneto-cardiograms and magneto-encephalograms, based on the use of superconducting Josephson elements, would come to every hospital. Magnetic cushions created by superconducting coils would support intercity express trains commuting at speeds of 400-500 km/h. In the lecture, the author tells about the history of superconductivity, briefly discusses the existing theories and, being its immediate participant , stops more in details on the last, fascinating, period of superconductivity investigations. A.A.Varlamov is the author of the monograph devoted to fluctuation phenomena in superconductors, he proposed the model of transverse transport in high temperature superconductors, studied properties of Josephson structures, granular superconductors and nano-scale superconducting systems.