| Popis: |
In this dissertation I have reported and discussed the results that suggest that superconductivity arises out of itinerant electron ferromagnetism in UGe2. Superconductivity is observed in the milli-Kelvin temperature range and close to but below the critical pressure where the Curie temperature collapses to absolute zero. This appears to be first example of this type of phenomena in Nature. A realistic model for the mechanism for pairing has not yet been developed for UGe2. We note, however, that a satisfactory description would have to explain not only the occurrence of superconductivity in a narrow pressure window just below the critical pressure, but also the unidentified transition at Tx which collapses to zero near the maximum of the superconducting transition temperature with pressure. A consistent model would also be expected to account for the divergence of the quadratic coefficient of the resistivity where Tx tends to absolute zero, and for the absence of superconductivity on the paramagnetic side of the border of ferromagnetism. An important clue to understanding the above properties may be found in the strong nesting which appears to exist on the majority skin part of the electron sheet of the Fermi surface. This nesting may be expected to produce a strong enhancement of the magnetic susceptibility at high wavevectors, particularly in the spin-polarised state. This should produce enhanced magnetic interactions, strongly coupled to charge and lattice fluctuations, again, particularly in the ferromagnetic state. It seems likely that pairing in the spin-triplet state will then emerge out of interactions which involve magnetic, charge and lattice degrees of freedom, which, in this case in particular, cannot be treated separately. The studies presented in this dissertation provide the groundwork for a comprehensive research programme to understand magnetic pairing in UGe2. Detailed investigations of the microscopic properties via bulk electronic and transport measurements and of the microscopic properties via neutron scattering are prime concerns of our future work. |
