Unconventional pairing in heavy Fermion metals
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The Fermi-liquid theory of superconductivity is applicable to a broad range of systems that are candidates for unconventional pairing,e.g. heavy fermion, organic and cuprate superconductors. Ginzburg-Landau theory provides a link between the thermodynamic properties of these superconductors and Fermi-liquid theory. The multiple superconducting phases of UPt3 illustrate the role that is played by the Ginzburg-Landau theory in interpreting these novel superconductors. Fundamental differences between unconventional and conventional anisotropic superconductors are illustrated by the unique effects that impurities have on the low-temperature transport properties of unconventional superconductors. For special classes of unconventional superconductors the low-temperature transport coefficients areuniversal, i.e. independent of the impurity concentration and scattering phase shift. The existence of a universal limit depends on the symmetry of the order parameter and is achieved at low temperatures κ B T ≪ γ ≪ Δ0, where γ is the bandwidth of the impurity induced Andreev bound states. In the case of UPt3 thermal conductivity measurements favor anE 1g orE 2u ground state. Measurements at ultra-low temperatures should distinguish different pairing states.
KeywordsFermi Surface Heavy Fermion Scatter Phase Shift Unconventional Superconductor Level Repulsion
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