Lifshitz transition enhanced triplet pz-wave superconductivity in hydrogen-doped KCr3As3

Abstract

The recently synthesized air-insensitive hydrogen-doped KCr3As3 superconductor has aroused great research interest. This material has, for the first time in the research area of the quasi-one-dimensional (quasi-1D) Cr-based superconductivity (SC), realized a tunability through charge doping, which will potentially significantly push the development of this area. Here, based on the band structure from first-principles calculations, we construct a six-band tight-binding model equipped with multiorbital Hubbard interactions and adopt the random-phase-approximation approach to study the hydrogen-doping dependence of the pairing symmetry and superconducting Tc. Under the rigid-band approximation, our pairing phase diagram is occupied by the triplet pz-wave pairing throughout the hydrogen-doping regime x∈(0.4,1) in which SC has been experimentally detected. Remarkably, the x dependence of Tc shows a peak at the three-dimensional–quasi-1D Lifshitz transition point, although the total density of states exhibits a dip there. The corresponding doping level is near the experimental estimation of the optimal doping level. A thorough investigation of the band structure reveals type-II van Hove singularities (VHSs) in the γ band, which favor the formation of the triplet SC. It turns out that the γ Fermi surface (FS) comprises two flat quasi-1D FS sheets almost parallel to the kz=0 plane and six almost perpendicular tubelike FS sheets, and the type-II VHS just lies in the boundary between these two FS parts. Furthermore, the |kz| of the van Hove planes reaches the maximum near the Lifshitz-transition point, which pushes the Tc of the pz-wave SC to the maximum. Our results appeal for more experimental access into this intriguing superconductor.

Source-reported materials — not catalogue approval

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