Unconventional superconductivity

Schematic pressure temperature phase diagram of UGe2. There are two ferromagnetic phases labelled FM1 and FM2 that differ in the magnitude of the ordered moment. At low temperatures, the transition between these phases is of first order (bold lines).

In a conventional picture of superconducting pairing, ferromagnetism and superconductivity do not coexist. The spectacular discovery of superconductivity in the ferromagnetic phase of UGe2 under pressure has therefore to be described in terms of a triplet spin-pairing mechanism for the superconducting state. As a main advance in this field, superconductivity has been discovered in the laboratory in another ferromagnet, URhGe, showing the phenomenon already at ambient pressure. Material development with single crystal growth of highest purity allows the investigation of the anisotropic properties of the superconducting state like critical currents and fields.
Neutron scattering studies are valuable tools to identify the possible role of magnetic excitations in the pairing mechanism of an unconventional superconducting state. Different systems have been investigated, such as the above mentioned ferromagnetic superconductors, the antiferromagnetically ordered superconductors Sr2RuO4 and UPd2Al3, and the high-TC cuprate superconductor La2-xSrxCuO4.
The study of the coexistence of superconductivity and antiferromagnetism in the doped spin-ladder system Sr14-xCaxCu24O41 at high pressures is of importance for the possible existence of a pairing mechanism based on attracting holes sharing the same rung on the ladder.
Among other investigated systems: MgB2, in which two distinct 2D and 3D Fermi surfaces contribute to superconductivity , and the skutterudites PrOs4Sb12 heavy fermion superconductor .

 

Last update : 10/11 2013 (288)

 

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