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.

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.

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.