Nonunitary Superconductivity in Complex Quantum Materials

Abstract

We present a comprehensive discussion on nonunitary superconductivity in complex quantum materials. Starting with a brief review of the notion of nonunitary superconductivity, we discuss its spectral signatures in simple models with only the spin as an internal degree of freedom. In complex materials with multiple internal degrees of freedom, there are many more possibilities for the development of nonunitary order parameters. We provide examples focusing on d-electron systems with two orbitals, applicable to a variety of materials. We discuss the consequences for the superconducting spectra, highlighting that gap openings of band crossings at finite energies can be attributed to a nonunitary order parameter if this is associated with a finite superconducting fitness matrix ${\hat{F}}_C(\mathbf{k})$. We speculate that nonunitary superconductivity in complex quantum materials is in fact very common and can be associated with multiple cases of time-reversal symmetry breaking superconductors.

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Cited by in corpus (7)

• Impurity-induced excitations in a topological two-dimensional ferromagnet/superconductor van der Waals moiré heterostructure
• Violation of the orbital depairing limit in a non-unitary state --on the high field phase in the heavy Fermion superconductor UTe${}_2$--
• Spin-orbit-coupled superconductivity with spin-singlet non-unitary pairing
• Spin susceptibility of nonunitary spin-triplet superconductors
• Nuclear spin relaxation rate of nonunitary Dirac and Weyl superconductors
• Nonequilibrium Green's function approach to multi-band Cooper-pair transport: linear magnetoresistance effect due to nonunitary superconductivity
• Sensitivity of superconducting states to the impurity location in layered materials