Exploring high transition temperature topological superconductivity in (Li1−xCoxOH)CoSb superlattices

Abstract

Among the FeSe-based superconductors, $({\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{OH})\mathrm{FeSe}$ has been discovered as an air-stable superlattice structure harboring both high transition temperature (high-${T}_{\mathrm{c}}$) superconductivity and intriguing topological superconducting properties. Here, we use first-principles approaches to identify a chemically isovalent and structurally identical counterpart of $({\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{OH})\mathrm{FeSe}$, namely, $({\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{OH})\mathrm{CoSb}$, which not only is an attractive candidate to harbor high-${T}_{\mathrm{c}}$ superconductivity, but also exhibits two distinct features surrounding topology and magnetism. The rationale of this predictive design is based on the recent identification of CoSb as a layered high-${T}_{\mathrm{c}}$ superconductor stabilized on ${\mathrm{SrTiO}}_{3}$. We first show that the superlattice structures of $({\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{OH})\mathrm{CoSb}$ $(x=0 \mathrm{or} 0.25)$ are dynamically and thermodynamically stable. Next, we demonstrate that $({\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{OH})\mathrm{CoSb}$ possesses superior superconducting properties to $({\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{OH})\mathrm{FeSe}$, offering an appealing platform for realizing high-${T}_{\mathrm{c}}$ superconductivity beyond the Cu- and Fe-based superconducting systems. More strikingly, we find that (LiOH)CoSb is already topologically nontrivial even without extrinsic doping in the spacer layers, thereby offering a cleaner and more ideal candidate system for realizing topological superconductivity. Furthermore, $({\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{OH})\mathrm{CoSb}$ exhibits weaker elemental magnetic moments than $({\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{OH})\mathrm{FeSe}$, which may provide a different angle for elucidating the microscopic mechanisms of superconductivity in these and related systems.