Magnetic pair-breaking effects

Strong magnetic pair-breaking effects have been reported for (Y,/ )Pd2B2C. Also in these compounds the drop in Tc follows de Gennes scaling, with the exception of R — Ce, Eu and Yb (Ghosh et al. 2001). 

However, the influence of magnetic and nonmagnetic impurities appears to be opposite for the SC and SDW critical temperatures (Tconset and T rder, respectively). While influence of nonmagnetic impurities at depression of Tynsef jn thg system is only negligible but in the SDW system normal impurities (say, Zn) produce the pair-breaking effect (for electron-hole pairs), the effect well known in excitonic semimetals. Such behavior is in fact... 

Similar effects have been obtained for the substitution of non-magnetic ions by magnetic ones. This concerns the strongly reduced Hc2 due to magnetic pair breaking (see, e.g., Takeya and El Massalami, 2004) and, additionally, the decreased positive curvature (Lan et al., 2000, 2001 Rathnayaka et al., 2003 see also... 

Toy] measured the Meissner effect in Cu-clad Nb wires doped with Fe down to 40 mK. They foxmd the thickness of the Meissner region in Cu to increase in proportion to 7, as in case of the normal impurity presence. The thickness was determined mainly by the electron mean free path in Cu and the interface between Cu and Nb. The dependence of thickness suggests the pair breaking effect weakens linearly with decreasing temperature below 1 K due to magnetic impurities. 

In both cases the RE-ions are in a non-magnetic ground state. A comparison with the corresponding data where Gd is replacing Tm and Tb shows effects of the type seen in fig. 17.22. For a detailed quantitative comparison one needs to know how the mean free path changes with impurity concentration since the pair-breaking effect (a) depends on it. 

Even weaker, yet very effective interaction is when the magnetic moment of the Pr ion couples with Cooper pairs and breaks them apart (pair breaking). 

We start from the Abrikosov-Gorkov theory and its predictions for Tc. In that theory the effect of the randomly distributed magnetic scattering centers of concentration m is characterized by a pair-breaking parameter o which is given by... 

The temperature dependence of the upper critical field in the presence of RE-impurities is determined by the following pair-breaking mechanisms a) the effect of the magnetic field acting on the electron orbits. This leads to Abrikosov flux lines in type II superconductors. This effect is mean free path dependent ... 

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