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Beilun Wu

Unconventional superconductivity in the ferromagnetic superconductor UCoGe

Published on 24 January 2017
Thesis presented January 24, 2017

This thesis mainly discuss the upper critical field of the ferromagnetic superconductor UCoGe. Thermal conductivity and other experimental methods have been used to confirm the numerous particular behaviors of Hc2 in UCoGe, previously observed in resistivity studies. These features, including the strong anisotropy and the anomalous curvatures, cannot be interpreted in terms of classical theories for Hc2. Instead, a phenomenon specific to the ferromagnetic superconductors - the field dependence of the pairing interaction, needs to be considered. We show that this effect can be consistently analyzed with normal phase properties, and is quantitatively compared with existing theory. This leads to a net clarification for the case of H//c in UCoGe, and at the same time explains the different behavior of Hc2 in UCoGe and URhGe. These results strongly support the magnetic origin of superconductivity in these systems. For H//b, we show convergent experimental observations that suggest a possible change of the superconducting state induced by the transverse magnetic field in UCoGe. Independent from the rest of the study, the last chapter presents some experimental results on the normal phase of UCoGe and on the other heavy-fermion system UBe13.

Key Pairing mechanism, Heavy Fermion, Unconventional superconductivity, Magnetism, UBe13

On-line thesis.