Fully gapped pairing state in spin-triplet superconductor UTe₂.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• UTe2 is a recently discovered superconductor with potential for spin-triplet superconductivity.
• The symmetry of its superconducting order parameter is currently debated.
• Previous studies suggested the presence of nodes in the superconducting gap.

Purpose of the Study:

• To determine the superconducting gap structure of ultraclean UTe2 single crystals.
• To investigate the symmetry of the superconducting order parameter.
• To clarify the topological nature of UTe2.

Main Methods:

• Measuring the thermal conductivity (κ/T) of ultraclean UTe2 single crystals at low temperatures.
• Applying magnetic fields along the a and c axes.
• Analyzing the reduction of nuclear magnetic resonance Knight shift.

Main Results:

• The a-axis thermal conductivity divided by temperature (κ/T) was found to be vanishingly small in the zero-temperature limit for magnetic fields along both a and c axes.
• This demonstrates the absence of nodes around the a axis, contradicting prior assumptions.
• The results, along with NMR Knight shift reduction, indicate an isotropic A representation and a fully gapped pairing state.

Conclusions:

• UTe2 likely possesses a fully gapped pairing state, belonging to the isotropic A representation.
• This suggests UTe2 is a three-dimensional strong topological superconductor.
• It may host helical Majorana surface states, analogous to superfluid 3He B phase.