Berlin 2024 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 67: Unconventional Superconductors

TT 67.8: Talk

Thursday, March 21, 2024, 11:45–12:00, H 3007

Thermodynamic transitions and topology of spin-triplet superconductivity: Application to UTe₂ — Henrik S. Røising, Max Geier, •Andreas Kreisel, and Brian M. Andersen — Niels Bohr Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark

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 non-unitarity 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 surfaces 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.

Keywords: triplet superconductivity; specific heat of superconductors; topological superconductivity; ab initio approaches