Unconventional superconductors

Many superconductors are suspected to be unconventional: the superconducting order parameter is believed to present a non-trivial structure and the superconducting "glue" may not be phonons, which are responsible for the formation of Cooper pairs in ordinary superconductors.

There are several families of unconventional superconductors:

High-Tc Cuprates
They are doped Mott insulators with a superconducting instability, which occurs at exceptionally high temperatures. Many experiments point to the d-wave symmetry of the order parameter. In spite of 25 years of world-wide research, what causes superconductivity is still a mystery. They continue to fascinate as they uniquely combine the technological promise of warm superconductivity with the intellectual challenge of frontier physics.

Heavy-fermions
These are metallic alloys with cerium, yterbium, uruanium or even transuranuim elements . They host correlated electrons with a very large effective mass. Superconductivity, with a non-trivial symmetry occurs in many of these sytems often close to a quantum critical point.

Organic salts
These are anisotropic metals made from organic molecules. Several families have been dicovered, often close to a competing instability. The symmetry of the order parameter is an unsettled issue. Phenomenologically, they present similarities with the other families.

Iron-based
Discovered quite recently, they are the first case of superconductivity above 50 K in absence of Mott physics. Superconductivity occurs near a magnetic instability and the order parameter is suspected to present a complex symmetry.

In our group, we study thermal and thermoelectric transport, often in extreme conditions, to explore both the normal and the superconducting states of these superconductors.

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