Electron pairs, lead compounds, small

Heavy Fermion superconductivity is found more frequently in intermetallic U-compounds than in Ce-compounds. This may be related to the different nature of heavy quasiparticles in U-compounds where the 5f-electrons have a considerable, though oibitally dependent, degree of delocalisation. The genuine Kondo mechanism is not appropriate for heavy quasiparticle formation as is the case in Ce-compounds. This may lead to more pronounced delocalised spin fiuctuations in U-compounds which mediate unconventional Cooper pair formation as discussed in sect. 2. The AF quantum critical point scenario invoked for Ce compounds previously also does not seem to be so important for U-compounds with the possible exception of UGe2. On the other hand AF order, mostly with small moments of the order 10 /Ub is frequently found to envelop and coexist with the SC phase in the B-T plane. 

Small amounts of organic compounds of low ionization potential (see Section 4.2) can be dissolved in liquefied rare gases. The solubility increases from argon to xenon. The scintillation light leads to single photon ionization from which electron/ion pairs originate. The electrons are detected in the usual manner with a charge-sensitive amplifier (see Section 2.10). This way the sensitivity and resolution of rare gas liquid detectors can be improved. Another method uses the scintillation photons to eject electrons from a photocathode (Aprile et al., 1994). 

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