Exploring High Transition Temperature Superconductivity in a Freestanding or SrTiO3 -Supported CoSb Monolayer

As a two-dimensional entity, FeSe has been widely explored to harbor high transition temperature (high-${T}_{c}$) superconductivity in diverse physical settings; yet to date, the underlying superconducting mechanisms are still under active debate. Here we use first-principles approaches to identify a chemically different yet structurally identical counterpart of FeSe, namely, monolayered CoSb, which is shown to be an attractive candidate to harbor high-${T}_{c}$ superconductivity as well. We first show that a freestanding CoSb monolayer can adopt the FeSe-like layered structure, even though its known bulk phase has no resemblance to layering. Next, we demonstrate that such a CoSb monolayer possesses superconducting properties comparable with or superior to FeSe, a striking finding that can be attributed to the isovalency nature of the two systems. More importantly, the layered CoSb structure can be stabilized on ${\mathrm{SrTiO}}_{3}(001)$, offering appealing alternative platforms for realizing high-${T}_{c}$ superconductivity beyond the well-established Cu- and Fe-based superconducting families. $\mathrm{CoSb}/{\mathrm{SrTiO}}_{3}(001)$ also exhibits distinctly different magnetic properties from $\mathrm{FeSe}/{\mathrm{SrTiO}}_{3}(001)$, which should provide a crucial new angle to elucidate the microscopic mechanisms of superconductivity in these and related systems.