Enhanced triplet superconductivity in next-generation ultraclean UTe2.

The unconventional superconductor UTe₂ exhibits numerous signatures of spin-triplet superconductivity--a rare state of matter which could enable quantum computation protected against decoherence. UTe₂ 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 UTe₂ 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 UTe₂ 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 UTe₂ between two distinct spin-triplet superconducting phases. [ABSTRACT FROM AUTHOR]