Higher-order topological phases for time-reversal-symmetry breaking superconductivity in UTe2

Abstract

The recent discovery of heavy-fermion superconductor UTe2 has broadened the possibility of realizing exotic time-reversal-symmetry breaking superconductivity. However, a comprehensive understanding of the topological phases in the superconducting states of UTe2 is still lacking. Here, we present an exhaustive classification of topological phases for all time-reversal-symmetry breaking pairing symmetries of UTe2. Using the K-theoretical classification approach, we uncover that 25 of 36 possible pairing states are classified as higher-order topological phases, with some demonstrating hybrid-order topology through an intricate interplay of hinge and corner states. Furthermore, under the weak-coupling condition of the pair potentials, the possible pairing symmetries are constrained to Bju+iBku, Au+iBju, and Bjg+iAu (j,k=1,2,3; j≠k), where these symbols denote the irreducible representations of the point group D2h. For these pairing states, the topological invariants are related to the Fermi surface topology via the Fermi-surface formula, enabling us to systematically diagnose higher-order topological phases. Using a tight-binding model, we demonstrate the higher-order topological phases of the mixed-parity Au+iB1g and nonunitary-odd-parity Au+iB1u superconductors, where the second-order and hybrid-order topological phases emerge as the number of Fermi surfaces enclosing the time-reversal invariant momentum evolves from two to four. The findings suggest that UTe2 serves as a compelling platform for exploring higher-order topological superconductors with diverse topological surface states.

Source-reported materials — not catalogue approval

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