Superconductors without inversion symmetry
Superconductivity in materials without inversion symmetry (NCS)
in the respective crystal structures occurs in the presence of an antisymmetric
spin-orbit coupling as a consequence of an emerging electric fi eld gradient.
The superconducting condensate is then a superposition of spin-singlet and
spin-triplet Cooper pairs. This scenario accounts for various experimental
findings such as nodes in the superconducting gap or extremely large upper
critical magnetic fields found in superconductors like CePt3Si or CeRhSi3.
Spin-triplet pairing can occur in a NCS environment in spite of Anderson's
theorem that spin-triplet pairing requires a crystal structure that exhibits
inversion symmetry. A central issue that arises when debating physical properties
of NCS superconductors pertains the role of strong correlations among electrons.