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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]

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]