Superconductors with magnetic impurities

Some properties of high field superconductors with magnetic impurities" (with G. Sarma), Solid State Commun.. 4, 449 (1966). 

The superconducting state can coexist with magnetic moments of localized electrons (e.g. of 4f type). It was experimentally found by Matthias et al. (1958a) that for rare-earth impurities substituted into a superconductor Tc rapidly decreases with increasing impurity concentration and that superconductivity is completely destroyed beyond a... 

Lan et al. (2000, 2001) and Lan (2001) report on Yi xR/xNi2B2C superconductors with R = Gd, Dy, Ho, Er. They found that the positive curvature of HC2(T) near Tc discussed in Section 6.2 for YxLui xNi2B2C also occurs in these compounds, i.e. the Rl magnetic moments do not cause a strong interband impurity scattering which might weaken the multiband character being responsible for the positive curvature of HC2(T) near Tc. 

Superconductivity [1.35]. Timgsten is a Type I superconductor with a transition temperature of 0.0154 0.0005 K. The critical magnetic field strength -> 0) is 1.15 0.03Oe. (91.5 A-m ). Impurities only show a minor influence on the transition... 

Keller and Fulde, 1973 Fulde and Peschel, 1972) for magnetic impurities with CEF-split ground states in superconductors without the introduction of Kondo mechanisms (McCallum et al., 1975a). 

Developments in crystal preparation techniques now make it possible to grow samples with a controlled amount of impurities. Both experimental and theoretical studies of the electromagnetic response in the presence of impurities have attracted a lot of attention. The primary motivation for these activities was to test the symmetry of the order parameter in cuprates. Such tests are possible since conventional superconductors (those with an isotropic s-wave gap) and exotic superconductors (those with a strongly anisotropic order parameter) are expected to behave diiferently in the presence of disorder (Sigrist and Ueda 1991). We will briefly review infrared results obtained in samples with non-magnetic and magnetic impurities in sect. 5.3. 

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