Enhanced triplet superconductivity in next-generation ultraclean UTe ₂

The unconventional superconductor UTe 2 exhibits numerous signatures of spin-triplet superconductivity—a rare state of matter which could enable quantum computation protected against decoherence. UTe 2 possesses a complex phase landscape comprising two magnetic field-induced superconducting phases, a metamagnetic transition to a field-polarized state, along with pair- and charge-density wave orders. However, contradictory reports between studies performed on UTe 2 specimens of varying quality have severely impeded theoretical efforts to understand the microscopic origins of the exotic superconductivity. Here, we report a comprehensive suite of high magnetic field measurements on a generation of pristine quality UTe 2 crystals. Our experiments reveal a significantly revised high magnetic field superconducting phase diagram in the ultraclean limit, showing a pronounced sensitivity of field-induced superconductivity to the presence of crystalline disorder. We employ a Ginzburg–Landau model that excellently captures this acute dependence on sample quality. Our results suggest that in close proximity to a field–induced metamagnetic transition the enhanced role of magnetic fluctuations—that are strongly suppressed by disorder—is likely responsible for tuning UTe 2 between two distinct spin-triplet superconducting phases.