Infrared properties of exotic superconductors

The infrared spectra of the non-traditional superconductors share certain c ommon features. The lack of a gap signature at 2 Delta and the residual con ductivity are the consequence of a d-wave order parameter. The high T-c mat erials, the organic conductors and the heavy Fermion materials have a stron g mid-infrared absorption band which can be interpreted as strong coupling of the carriers to electronic degrees of freedom, which leads to a breakdow n of the Fermi liquid picture. The cuprates and the organic charge transfer salts are unique in possessing an intrinsic low dimensionality. The charge transport normal to the highly conducting direction is incoherent down to the lowest temperatures and frequencies. (C) 1999 Elsevier Science B.V. All rights reserved.