Clean-limit superconductor

It should be noted that within the BCS theory one does not expect to observe any explicit correlation between and the superfluid density in a clean-limit superconductor. The linear dependence between the transition temperature and tis/m is expected if... 

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 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... 

Raman spectroscopy is also capable of probing the pseudogap. In conventional superconductors, the Raman spectrum only shows a peak at the pair-breaking frequency 2A (Abrikosov and Fal kovskii 1961). In the clean limit no other absorption is expected apart from a very low frequency band from free electrons, but in the cuprates, because of the strong incoherent scattering (Shastry and Shraiman 1990), a broad continuum appears that gives rise to a constant Raman background up to 2 eV (Varma et al. 1989). 

A survey of the literature (Hagen et al. 1993) has indicated that, in general, the anomalous Hall behavior is present among moderately clean superconductors (// 0.5-5, where / is the transport mean free path and is the coherence length), but does not occur in either the very clean (// 1) or dirty (// 1) limits. Colino... 

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