Review of U-based Ferromagnetic Superconductors: Comparison between UGe2, URhGe, and UCoGe

The discovery in 2000 that the ferromagnetic (FM) compound UGe2 (TCurie = 52 K at ambient pressure) becomes superconducting under a pressure of P = 1.1 GPa until it enters the paramagnetic (PM) phase above Pc = 1.6 GPa was a surprise, despite the fact that such a possibility was emphasized in theory four decades ago. Successive searches for new materials (URhGe and UCoGe) led to the discovery of the coexistence of superconductivity (SC) and ferromagnetism at ambient pressure. Furthermore in UCoGe, it was found that SC survives in the PM regime from Pc = 1.1 to 4 GPa. The novelty is that SC also emerges deep inside the FM regime but with strong FM fluctuations. Focus has been on low-temperature experiments under extreme conditions of magnetic field (H), pressure, and uniaxial stress. NQR and NMR experiments are unique tools to understand the interplay between the spin dynamics and the Cooper pairing. We choose to present the SC properties from the knowledge of quasiparticle dressing in the normal phase (re...