Clean limit

Analytical Method/Cleaning Limits Processing and Filling Processing... 

Here we will summarize, from the previous subsections as well as from literature, some typical properties and representative parameters (see table 6) of the superconducting state of YNi2B2C and LuNi2B2C where completeness is not attempted. These materials are usually clean-limit type II superconductors. However by substitutional disorder on the rare earth site in (Y,Lu)Ni2B2C or on the transition-metal site in Lu(Ni,Co)2B2C the residual resistance ratio RRR = p(300 K)/p(Tc), where p(T) is the normal state resistivity, and the mean free path / of the electrons in the normal state can be considerably reduced... 

The multiband superconductivity shows up only in the clean limit , where the single electron mean free path for the interband impurity scattering satisfies the condition / > hvF/Aav where vF is the Fermi velocity and Aav is the average superconducting gap [24,28,30,35],... 

The interband pairing term enhances Tc [93-97,102] by tuning the chemical potential in an energy window around the Van Hove singularities, z =0, associated with a change of the topology of the Fermi surface from ID to 2D (or 2D to 3D) of one of the subbands of the superlattice in the clean limit. 

These results show that the two gaps behaviour is present over all the range of the reduced Lifshitz parameter -0.8< z <+0.8. These results support the predictions that the doped materials remain in the clean limit for interband pairing although the large number density of impurity centres. This results falsifies the predictions of the multigap suppression because of impurity scattering due to substitutions. 

The non-local effects can result in an anisotropy of Hc2 microscopically due to the anisotropy of the pairing state (Shiraishi et al., 1999) or directly to the anisotropy in the shape of the Fermi surface (Metlushko et al., 1997). The anisotropy of the Fermi surface sheets (see Section 3.2) has been assumed to cause the mentioned basal anisotropy of Hc2 because the borocarbide superconductors are usually clean-limit type-II superconductors. In the clean limit for an anisotropic Fermi surface the non-local corrections to Hc2 are given by... 

In both these special cases, A6/A2 is independent of disorder.[Haas et al., 1997] A variation of A6/A2 can, therefore, only be expected for a2 / a6 and Ag6 A22A66- However, since A6/A2 depends only on j/2 — ir6 the variation remains modest even for Tc —> 0. The inset of Fig. 1 gives an example of the variation of A6/A2 with F and So. The main panel shows the transition temperature normalized to its clean limit value as function of the scattering rate, normalized to the critical scattering rate for pure. v-wavc scattering Tcrit = 0.882 7co, for three values of the scattering phase shift. In the case of... 

Figure 2.34 illustrates these serious experimental problems. In the upper part (a) the magnetic penetration depth of k-(ET)2Cu(NCS)2 measured by ac susceptibility [220] and in the lower part (b) the same quantity obtained by dc magnetization [227] is shown. The clear discrepancy of the behavior of A(T) at low temperatures is obvious. In the ac-susceptibility experiment consistent with [221, 222, 223] a variation is found. This non-exponential non-BCS dependence can be explained with energy-gap nodes of several different topologies [222]. On the other hand, the data of [227] could very well be described by conventional weak-coupUng theory in the clean limit as shown... 

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