Thermodynamic transitions and topology of spin-triplet superconductivity: Application to UTe${}_2$

Abstract

The discovery of unconventional superconductivity in the heavy-fermion material UTe${}_2$ 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 surface states producing chiral Majorana hinge modes. DFT+$U$ band-structure calculations support that these topological phases are realized in UTe${}_2$ when introducing weak superconducting pairing. Our topological analysis suggests measurable signatures for surface-probe experiments to acquire further evidence of the superconducting pairing symmetry.

20 pages, 8 figures

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• Theoretical studies on off-axis phase diagrams and Knight shifts in UTe${}_2$ -- Tetra-critical point, d-vector rotation, and multiple phases
• Higher-order topological phases for time-reversal-symmetry breaking superconductivity in UTe${}_2$
• Revealing isotropic abundant low-energy excitations in UTe${}_2$ through complex microwave surface impedance
• Euler band topology in superfluids and superconductors
• A unified theoretical framework for Kondo superconductors: Periodic Anderson impurities with attractive pairing and Rashba spin-orbit coupling
• Electronic structure of UTe${}_2$ under pressure
• Quasiparticle Interference of Spin-Triplet Superconductors: Application to UTe${}_2$
• Theoretical Study of Impurity Effects on Superconductivity in UTe2