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le 25 avril 2011
The twentieth century was replete with profound new discoveries in Physics that radically reshaped the way we think about the world around us. In a nutshell, we can think of these conceptual breakthroughs in terms of two simple slogans: "small is different" and "more is different." "Small is different" refers to the fact that when we look at the world at the very smallest scale the usual laws of everyday Physics start to break down. We are unable to determine position of objects with any finite certainty, objects seem to be able to be at two possible locations at a same time, and properties of objects don't vary smoothly but come in terms of discrete values. The realm of the very smallest is investigated in the parts of Physics that we call Quantum Mechanics (see for instance Quantum Theory: A Very Short Introduction (Very Short Introductions)) and Particle Physics (see for instance Particle Physics: A Very Short Introduction. When we think of modern Physics, this is usually what we first have in mind. However, another important conceptual line of investigation is encapsulated in the other phrase, "more is different." This refers to the fact that many times, a whole is greater than the sum of its parts, and under certain conditions it is impossible to understand the behavior of a system of particles just by understanding the properties of individual particles. In fact, in some cases the notion of individual particle itself becomes suspect. Quantum mechanics itself has already hinted at some of this, but the branch of Physics that are deals with this approach to the world around us the most is called "Solid State Physics" or "Condensed Matter Physics." This is an area of vast and important active research, both theoretical and experimental, but it has never quite gotten the public recognition that it warrants. For instance Jim Bardeen, the only person to have won the Nobel Prize in Physics twice, is hardly a household name. This very short introduction is a good starting point to get acquainted with one phenomenon that the Condensed Matter Physics deals with, and that is the phenomenon of Superconductivity.
Superconductivity is the property of certain materials that endows them with perfect conductivity at very low temperatures. Since the temperatures at which it manifests itself are extremely low, until the early part of twentieth century it was a completely unknown phenomenon. The first chapter or so of this book deal with the search for the very low temperatures, and the significant milestones along that way. We are then shown how the search for these low temperatures lead to the discovery of some very interesting properties of metals at those extreme regimes, among which was superconductivity. The first part of the twentieth century was spent at discovery and better characterization of superconducting materials, primarily metals, but a theoretical understanding of superconductivity proved much more elusive. A breakthrough happened in 1950s, when aforementioned John Bardeen with a couple of his collaborators came up with a theory of "regular" superconductivity, i.e. the kind of superconductivity that was known to exist up through 1980s. And then, in 1980s superconductivity was discovered in all sorts of unexpected places, and many of the materials that it was discovered in were not even metals. The theory of this so-called high-temperature superconductivity has to this day eluded researchers.
What makes superconductivity so important to study is the fact that it is the ultimate many-body phenomenon: superconductivity cannot be reduced to conduction of individual electrons, but all of the electrons in a material must be taken into the account at once, together with their interaction with the rest of the material. This is what makes understanding superconductivity intrinsically difficult.
The book concludes with several applications of superconductivity and prospects for future research and discovery. This is a very well written book that makes a very difficult subject accessible to the general audience.