Enhanced triplet superconductivity in next generation ultraclean UTe2

TL;DR

This study reveals that ultra-clean UTe$_2$ crystals exhibit a significantly different high magnetic field superconducting phase diagram, highlighting the crucial role of magnetic fluctuations and sample purity in stabilizing spin-triplet superconductivity.

Contribution

The paper provides the first comprehensive high-field measurements on pristine UTe$_2$, demonstrating the impact of crystalline disorder on its exotic superconducting phases and refining the phase diagram.

Findings

Superconducting phases are highly sensitive to sample quality.

Disorder suppresses magnetic fluctuations critical for superconductivity.

A revised phase diagram shows new high-field superconducting behavior.

Abstract

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-polarised 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 new 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.