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Register a new userFirst-principles based theory of spin-orbit coupling induced triplet pairing: Application to the superconducting ground state of rhenium
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Recent $mu$SR measurements revealed that spontaneous magnetism exists in the superconducting state of rhenium and it also appears in other rhenium based materials like Re$_6$Zr, Re$_6$Hf, Re$_6$Ti. The superconducting state of these materials show $s$-wave-like properties and the pairing mechanism is most likely driven by electron-phonon coupling. In this paper we take elemental rhenium as a testbed and investigate its ground state. By developing an LCAO formalism for the solution of the spin-generalized Bogoliubov-de Gennes equation we use every details of the first-principles band-structure together with spin-orbit coupling. In this paper we provide a possible explanation of the spontaneous time-reverseal symmetry breaking in the superconducting ground state of rhenium by arguing that taking into account the orbital degrees of freedom, spin-orbit coupling is inducing even-parity odd-orbital spin triplet Cooper pairs, and Cooper pairs migration between the equal-spin triplet states may lower the total energy. We show how magnetism emerges and the structure of the gap changes as a function of the triplet component of the interaction strength.
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Motivated by the recent findings of unconventional superconductivity in $mathrm{CoSi_2 / TiSi_2}$ heterostructures, we study the effect of interface induced Rashba spin orbit coupling on the conductance of a three terminal T shape superconducting device. We calculate the differential conductance for this device within the quasi-classical formalism that includes the mixing of triplet-singlet pairing due to the Rashba spin orbit coupling. We discuss our result in the light of the conductance spectra reported by Chiu {it et al.} for $mathrm{CoSi_2 / TiSi_2}$ heterostructures.
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Motivated by the possible non-spin-singlet superconductivity in the magic-angle twisted trilayer graphene experiment, we investigate the triplet-pairing superconductivity arising from a correlation-induced spin-fermion model on a honeycomb lattice. We find that the $f$-wave pairing is favored due to the valley-sublattice structure, and the superconducting state is time-reversal symmetric, fully gapped, and non-topological. With a small in-plane magnetic field, the superconducting state becomes partially polarized, and the transition temperature can be slightly enhanced. Our results apply qualitatively for the triplet-pairing superconductivity in graphene-based moire systems, which is fundamentally distinct from triplet superconductivity in $^3$He and ferromagnetic superconductors.
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