Theory of triplet pairing and surface states in UTe2

The discovery of unconventional superconductivity in the heavy-fermion material UTe2 has reinvigorated research of spin-triplet superconductivity with attempts to pinpoint the superconducting order parameter. From a theoretical side, we study several pairing states among them also non-unitary ones and their thermodynamic transitions into the superconducting state. With focus on the behavior of the temperature dependence of the specific heat capacity, we find that the onset non-unitary order pairing may feature vanishing or even negative secondary specific heat anomalies. In a minimal microscopic model that captures the U and Te Fermi surface sheets we incorporate (Au) Bu phases which generates (full gap) point node superconducting states. We perform an analysis of the topological surface states associated with the different possible spin-triplet orders: single-component orders host Majorana Dirac surface states in addition to possible bulk nodes. A second component breaking time-reversal symmetry gaps these surface states producing chiral Majorana hinge modes. Our topological analysis suggests measurable signatures for surface-probe experiments to acquire further evidence of the superconducting pairing symmetry. We also present the results of the local density of states in the presence of vortices. The interplay between the topological surface states and the vortex bound states leads to signatures in the surface density of states which could help to further pinpoint the realized order parameter in UTe2. Finally, we discuss possible scenarios for disorder-induced time-reversal symmetry breaking in UTe2.