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De Gennes
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Aimant

Pierre-Gilles de Gennes

France, 1932 - 2007

Rights reservedPierre Gilles de Gennes (1932- 2007) was a French physicist who won the Nobel Prize in 1991 thanks to his discoveries on liquid crystals and polymers. He is also known for his works on superconductivity in the 60s, which made the group he led at the faculté d’Orsay worldly famous.

In 1959, after his PhD at the CEA on magnetism in metals and alloys, de Gennes joined the laboratoire de physique des solides d’Orsay that had just been created by A. Guinier, J. Friedel and R. Castaing. In this new environment, he studied superconductors, shortly after Bardeen, Cooper and Schrieffer developed their theory in the United States. At the same time, the Soviets Abrikosov and Gorkov were studying the magnetic properties of superconductors: the disappearance of superconductivity in presence of a weak iron atom concentration, for instance, is caused by the fact that the electron pairs responsible for superconductivity are “broken” by magnetic interaction.

De Gennes also studied magnetic interactions in superconductors but that time, he used a magnetic field to break the electron pairs. In type II superconductors, such as non-magnetic superconducting alloys, the magnetic field penetrates the material under the form of a regular pattern of lines and whirlwinds in which superconductivity is cancelled. De Gennes then conducted a wonderful experiment in Saclay with D. Cribier and B. Jacrot using neutron diffusion, which clearly showed this whirlwind pattern.

With Daniel Saint James, a physicist in Saclay, he discovered that above the superior magnetic field for which magnetic interactions cancel superconductivity in a massive material, called Bc2, superconductivity persists up to a superior magnetic field Bc3= 1,69Bc2 in the proximity of a free surface.

It was in Orsay however that he continued his studies along with a group he created and called groupe de supraconductivité d’Orsay, composed of an experimental team of four researchers – his “musketeers”, which include the author of this article – and a few theoreticians. He used his master’s degree classes to write a book, superconductivity of metals and alloys, which is still a reference book today.

The studies made by the experimental group, mainly on thin metal layers, highlighted surface superconductivity and other theories of de Gennes, such as the absence of forbidden lines in superconductor with a high magnetic field thanks to tunnel effect experiments, the possibility of inducing superconductivity in a normal metal in proximity of a superconducting layer, etc. The main research characteristic created by de Gennes that attracted physicists of that particular domain between 1960 and 1968 was the teamwork he invented, bringing together experimenters and theoreticians, with a humble conductor who put the students inspired by his works before him.

De Gennes then studied soft matter, focusing on liquid crystals and polymers. He drew parallels with the concepts he had used to describe transitions between orderly and non-orderly states in the solids he had studied, such as superconductors and ferromagnets, for which he won the Nobel Prize in 1991.

CNRSSociété Française de PhysiqueTriangle de la physique
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CNRSSociété Française de PhysiqueTriangle de la physique