Chiral superconductivity in UTe2 probed by anisotropic low-energy excitations

The new uranium‐based superconductor UTe₂ attracts much interest as a paramagnetic analog of ferromagnetic superconductors. The extremely high upper critical field along the magnetic hard axis, reentrant superconductivity, and only a small reduction of the Knight shift in UTe₂ indicate the spin‐triplet superconducting state likely mediated by ferromagnetic fluctuations. Furthermore, scanning tunneling spectroscopy and optical Kerr effect measurements suggest a chiral superconducting state with topologically nontrivial surface states. Focusing on the superconducting gap, previous experimental studies reported the gap structure with point nodes which is consistent with the spin‐triplet superconductivity. However, the positions of the point nodes, which are quite important to confirm the multicomponent superconducting order parameter and superconducting symmetry, are still unrevealed. Thus, we performed the magnetic penetration depth measurements with the magnetic field along each crystallographic axis to detect the anisotropy of the low‐energy excitations, from which we can estimate the positions of the point nodes. Based on our results, we can rule out the single component order parameters, and we find that the most plausible superconducting state is a chiral B_3u+iA_u state, which provides fundamentals of the topological properties in UTe₂.