Multiple superconducting phases in a nearly ferromagnetic system

The nearly ferromagnetic superconductor UTe 2 shows several intriguing phenomena, including an extraordinary reinforcement of superconductivity in very strong magnetic fields. Here we show that pressure tunes the system to a more correlated state and probable magnetic order. The superconducting critical temperature is also strongly enhanced, reaching almost 3 K, a new record for U-based heavy fermion superconductors. Most spectacularly under pressure we find a transition within the superconducting state, putting UTe 2 among the very rare systems having multiple superconducting phases. UTe 2 under pressure is a treasure trove of several of the most fascinating phenomena in unconventional superconductivity and may well be a keystone in their understanding. The recent discovery of superconductivity with an unusually high upper critical field in the heavy fermion system UTe2 has incited enormous interest in this material as one of the rare known spin-triplet superconductors with potentials for topological superconductivity and quantum computing. In this work, the authors report evidence for enhanced superconductivity and multiple superconducting phases in UTe2 under hydrostatic pressure, revealing a very rich phase landscape in this material.