Thermodynamic transitions and topology of spin-triplet superconductivity: Application to UTe2

The discovery of unconventional superconductivity in the heavy-fermion material UTe2 has reinvigorated research of spin -triplet superconductivity. We perform a theoretical study of coupled two -component spin -triplet superconducting order parameters 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 two -component time -reversal symmetry breaking superconducting order may feature vanishing or even negative secondary specific heat anomalies. The origin of this unusual specific heat behavior is tied to the nonunitarity of the composite order parameter. Additionally, we supply an analysis of the topological surface states associated with the different possible spin -triplet orders: single -component orders host Dirac Majorana surface states in addition to possible bulk nodes. A second component breaking time -reversal symmetry gaps these surface states producing chiral Majorana hinge modes. DFT + U band -structure calculations support that these topological phases are realized in UTe2 when introducing weak superconducting pairing. Our topological analysis suggests measurable signatures for surface -probe experiments to acquire further evidence of the superconducting pairing symmetry.