Thermodynamics investigation of the superconducting phase in UCoGe

UCoGe is one of the few superconductors where ferromagnetism and superconductivity microscopically coexist, making it a strong candidate to p-wave superconductivity. It also displays very high critical field (>15 T) despite relatively low T_sc≈ 0.550 K. The recent discoveries of multiple superconducting phases in UTe₂ and CeRh₂As₂ at ambient pressure have revived the question of the presence of different superconducting phases in UCoGe, which is still unsettled due to the scarcity of thermodynamics measurements carried out in the past.

Here we present the first complete (3 axes) phase diagram established from specific heat measurements. We recover the already known strong anisotropy of the critical field due to the tuning of the pairing mechanism by the magnetic field.

More surprisingly, our specific heat measurements reveal an anomalous behavior of the specific heat jump. We will discuss the possible origins of this anomalous behavior in UCoGe, and notably the relation with the superconducting pairing mechanism.