Chiral superconductivity in heavy-fermion metal UTe2

Abstract

Spin-triplet superconductors are condensates of electron pairs with spin 1 and an odd-parity wavefunction¹. An interesting manifestation of triplet pairing is the chiral p-wave state, which is topologically non-trivial and provides a natural platform for realizing Majorana edge modes^2,3. However, triplet pairing is rare in solid-state systems and has not been unambiguously identified in any bulk compound so far. Given that pairing is usually mediated by ferromagnetic spin fluctuations, uranium-based heavy-fermion systems containing f-electron elements, which can harbour both strong correlations and magnetism, are considered ideal candidates for realizing spin-triplet superconductivity⁴. Here we present scanning tunnelling microscopy studies of the recently discovered heavy-fermion superconductor UTe₂, which has a superconducting transition temperature of 1.6 kelvin⁵. We find signatures of coexisting Kondo effect and superconductivity that show competing spatial modulations within one unit cell. Scanning tunnelling spectroscopy at step edges reveals signatures of chiral in-gap states, which have been predicted to exist at the boundaries of topological superconductors. Combined with existing data that indicate triplet pairing in UTe₂, the presence of chiral states suggests that UTe₂ is a strong candidate for chiral-triplet topological superconductivity.