Point-node gap structure of the spin-triplet superconductor UTe₂

Area of Science:

• Condensed Matter Physics
• Superconductivity Research
• Actinide Materials Science

Background:

• UTe2 is an actinide superconductor with unique properties.
• Understanding the superconducting energy gap is crucial for classifying its unconventional nature.

Purpose of the Study:

• To determine the structure of the superconducting energy gap in UTe2.
• To investigate the unconventional spin-triplet superconducting order parameter.

Main Methods:

• Low-temperature electrical and thermal transport measurements.
• Magnetic penetration depth and heat capacity measurements.
• Crystallographic transport analysis along a and b axes.

Main Results:

• Vanishing residual fermionic thermal conductivity observed.
• Evidence for nodal quasiparticles and a point-node gap structure.
• Quadratic temperature dependence of magnetic penetration depth up to T/Tc = 0.3.
• Upturn in specific heat below 300 mK attributed to quantum-critical DOS.

Conclusions:

• Measurements strongly support an unconventional spin-triplet superconducting order parameter with point nodes in UTe2.
• The findings are consistent across thermal conductivity, penetration depth, and specific heat data.
• A cubic power law for the electronic DOS below Tc aligns with the point-node gap structure.