Distinguishingd-wave superconductors from highly anisotropics-wave superconductors

Gap symmetry of superconducting borocarbide YNi2B2C and skutterudite PrOs4Sb12

“…3 is well approximated by ω g (Γ) = Γ/(1 + 2Γ ∆ ). This immediate opening of the energy gap is very different from the case of s+d-wave superconductors as discussed in [36]. This has immediate consequences: There are no nodal excitations for T < Γ.…”

“…In this respect the superconductivity in YNi 2 B 2 C and LuNi 2 B 2 C is of great interest in part due to their relatively high transition temperature 15.5 K and 16.5 K resepectively [34]. Although the dominance of s-wave component in ∆(k) has been established by substituting Ni by a small amount of Pt and subsequent opening of the energy gap [35,36], the superconductivity exhibits many characteristics of nodal superconductors like T 3 behaviour of T −1 1 and the √ H-dependence of the specific heat [38]. Due to their tetragonal space group I4/mmm the borocarbides have fourfold rotational symmetry within the a-b plane.…”

Anisotropics-wave superconductivity in borocarbidesLuNi2B2CandMaki1, Thalmeier2, Won3 2002Phys. Rev. B

“…Although the dominance of the s-wave component in ∆(k) has been established by substituting Ni by a small amount of Pt and subsequent opening of the energy gap 4,5 , a number of peculiarities are not expected in a conventional s-wave superconductor 6 . For example the √ H dependence of the specific heat in the vortex state indicates a superconducting state with nodal excitations similar to dwave superconductivity in high T c cuprates 7,8,9,10 .…”

Transport properties of extended-s-state superconductors

“…d-wave, see Figure 1a) have been put forward, 2] it is interesting to consider the consequences of the simpler suggestion that k has the full symmetry of the crystal, but changes sign (see Figure 1b). Fehrenbacher and Norman 3] have considered the e ects of potential scattering on such a state, following earlier work on anisotropic-s states with nodes, 4,5] and shown that small concentrations of impurities can lead to \gap-less" behavior in the density of states (i.e., with residual density of states N(0) > 0), followed by the opening of an actual induced gap in the quasiparticle spectrum as the concentration is increased further. The prediction of a range of impurity concentrations over which \gapless" behavior is predicted is important because microwave and NMR experiments, particularly on Zn and Ni-doped YBCO crystals 6,7] have shown evidence of low-temperature thermodynamic properties re ecting the existence of a residual density of states.…”