Magnetic Confinement of Spin-Triplet Superconductivity*

Electrical magnetoresistance and tunnel diode oscillator measurements were performed under external magnetic fields up to 41T applied along the crystallographic b axis (hard axis) of UTe₂ as a function of temperature and applied pressures up to 18.8kbar. In this work, we track the field-induced first-order transition between superconducting and magnetic field-polarized phases as a function of applied pressure, showing suppression of the transition with increasing pressure until the demise of superconductivity near 16kbar and the appearance of a pressure-induced ferromagnetic-like ground state that is distinct from the field-polarized phase and stable at zero field. Together with evidence for the evolution of a second superconducting phase and its upper critical field with pressure, we examine the confinement of superconductivity by two orthogonal magnetic phases and the implications for understanding the boundaries of triplet superconductivity.