Fig. 4: Dirac-fermion-assisted interfacial superconductivity in (Bi_1-xSb_x)₂Te₃/FeTe heterostructures.

a–c The Sb concentration x dependence of the Fermi momentum k_F (a), the onset of superconducting transition temperature T_{c, onset} (blue squares) and the superconducting transition temperature with the zero resistance T_c,0 (red circles) (b), and the upper critical magnetic field μ₀\({H}_{{{{{{\rm{c}}}}}}2,\perp }\) (c). The error bars in (a) are estimated from the width of the surface state at k_F. The error bars in (b) are estimated to be ~20% of (T_{c, onset} - T_c,0). The error bars in (c) are estimated to be ~40% of [μ₀\({H}_{{{{{{\rm{c}}}}}}2,\perp }\)(R_normal)- μ₀\({H}_{{{{{{\rm{c}}}}}}2,\perp }\)(R ~ 0.5R_normal)]. d A phenomenological interpretation of the Dirac-fermion-assisted interfacial superconductivity in (Bi_1-xSb_x)₂Te₃/FeTe heterostructures. The left panel shows the bicollinear antiferromagnetic order of the FeTe layer. \({J}_{i}\) with \(i={{{{\mathrm{1,2,3}}}}}\) are spin-spin interactions. The middle panel shows the spin-exchange coupling between itinerant Dirac electrons and local spins of FeTe, resulting in the RKKY interaction between two magnetic moments. The right panel shows a possible renormalized spin model in FeTe with a suppressed antiferromagnetic order. e The Dirac fermion-induced RKKY interaction \({J}_{{RKKY}}({k}_{F}{R}_{{ij}})\). Here \({R}_{{ij}}\) is the next nearest bond of irons, and it reaches its minimal for \({k}_{F}\) ~ 0 near \(x\approx 0.85\). The error bars in (e) are estimated through the calculation of both \({J}_{{RKKY}}\left({k}_{F}-\Delta {k}_{F}\right)\) and \({J}_{{RKKY}}\left({k}_{F}+\Delta {k}_{F}\right)\), mirroring the error bars in (a). f The possible \({s}_{\pm }\)-wave pairing symmetry in real and momentum spaces.