The pressure-temperature phase diagram of the orthorhombic ferromagnetic superconductor UCoGe was determined by resistivity measurements up to $10.5\mathrm{GPa}$. The Curie temperature $T_C$ is suppressed with pressure and vanishes at the critical pressure $p_c\approx 1\mathrm{GPa}$. Superconductivity is observed in both the ferromagnetic state at low pressure, and in the paramagnetic state above $p_c$ up to about $4\mathrm{GPa}$. Non-Fermi-liquid behavior appears in a large pressure range. The resistivity varies linearly with temperature around $p_c$ and evolves continuously with pressure to a $T^2$ Fermi-liquid behavior for $p⪆5$ GPa. The residual resistivity as a function of pressure shows a maximum far above $p_c$ at $p^{☆}=7.2\mathrm{GPa}$ and the amplitude of the inelastic scattering term of the resistivity decreases by more than one order in magnitude at $p^{☆}$, which appears to mark the entrance into a weakly correlated regime. The pressure dependence of the upper critical field for magnetic field applied along the $b$ and $c$ axis illustrates the drastic difference in the field dependence of the ferromagnetic superconducting pairing. While for $H\parallel b$ axis $H_{c2}\left(T\right)$ is driven by the suppression of the ferromagnetic order, it is dominated by the strong initial suppression of the ferromagnetic fluctuations for a field applied in the easy magnetization axis $c$.

• Received 25 May 2016
• Revised 3 August 2016

DOI:https://doi.org/10.1103/PhysRevB.94.125110