I will spend some time discussing the specific scientific tools that de Gennes used for his studies of magnetism, superconductivity, liquid crystals, polymers, soft condensed matter, and biology. Some recurrent items can be found.

  • His interest in order/disorder effects in condensed matter as well as the essential role of defects in such structures. These defects should be avoided in some instances. In other cases, such as semiconductor electronics or properties of metal and alloys, they play an essential role.

  • The use of analogy is a key that opens corridors between different rooms of science. Its use requires rigor and precise comparisons between different problems and should not be confused with loose metaphors. A mastery of analogy helped de Gennes build strong bridges between magnetism, superconductivity, liquid crystals, and polymers.

  • Interfaces are another theme in de Gennes’ research. Borders separate different entities, but they should also allow exchanges across them. It is possible in physics to transfer properties from one layer into an adjacent layer by such proximity effects. In such cases, original behaviors will emerge from this interplay. This type of geometry has been often considered by de Gennes in his work. It is also the basic principle behind the Nobel prize awarded to a “normalien” (as de Gennes was), Albert Fert, in 2007: by putting together stacks of very fine layers of a good conductor (copper) and of poorly-conducting magnetic iron layers, he was able to obtain some very anomalous magneto-conducting effects that are ubiquitous in today’s memory chips of our computers and portable phones.

Quite metaphorically, we could say that these various properties—dialogue between order and disorder, the presence and role of defects, and the interactions at interfaces—are all elements of society! These scientific tools, having a large scope of application

ure—the meter or the kilogram—in order to provide a common reference that could be shared among all citizens.

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