Observation of odd-parity superconductivity in UTe₂

Area of Science:

• Condensed Matter Physics
• Superconductivity Research
• Materials Science

Background:

• Superconducting order parameter symmetry is crucial for understanding material properties.
• UTe2 exhibits a high upper critical field and reentrant behavior, suggesting spin-triplet pairing.
• Experimental confirmation of spin-triplet symmetry in UTe2, particularly at low fields, remains elusive.

Purpose of the Study:

• To experimentally determine the orbital symmetry of the superconducting order parameter in UTe2.
• To provide phase-sensitive evidence for the spin-triplet nature of UTe2 superconductivity.
• To investigate the presence of Andreev surface bound states in UTe2.

Main Methods:

• Utilizing the Josephson effect for phase-sensitive measurements.
• Employing orientation-dependent Josephson coupling between an s-wave superconductor (Indium) and UTe2.
• Surface-sensitive probes to detect Andreev bound states.

Main Results:

• The orientation dependence of Josephson coupling strongly indicates an odd-parity B1u pairing state in UTe2 near zero magnetic field.
• This finding provides robust evidence for UTe2 being a spin-triplet superconductor.
• Apparent formation of Andreev surface bound states was observed on the (1-10) surface.

Conclusions:

• UTe2 exhibits an odd-parity, spin-triplet superconducting state, specifically B1u symmetry, at low magnetic fields.
• The Josephson effect measurements provide the first unambiguous, phase-sensitive evidence for this pairing symmetry.
• The observation of Andreev surface bound states offers further insights into the unconventional nature of UTe2 superconductivity.