In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors in which superconductivity coexists with magnetism, and a few examples are known where the superconductivity itself induces spontaneous magnetism. The best known of these compounds are Sr₂RuO₄ and some non-centrosymmetric superconductors. Here, we report the finding of a narrow dome of an \(s+is^{\prime}\) superconducting phase with apparent broken time-reversal symmetry (BTRS) inside the broad s-wave superconducting region of the centrosymmetric multiband superconductor Ba_1 − xK_xFe₂As₂ (0.7 ≲ x ≲ 0.85). We observe spontaneous magnetic fields inside this dome using the muon spin relaxation (μSR) technique. Furthermore, our detailed specific heat study reveals that the BTRS dome appears very close to a change in the topology of the Fermi surface. With this, we experimentally demonstrate the likely emergence of a novel quantum state due to topological changes of the electronic system.

通常，磁性和超导性是相互对抗的。然而，存在超导与磁性共存的超导体的几个家族，并且已知一些超导本身引起自发磁性的例子。这些化合物中最著名的是Sr ₂ RuO ₄和一些非中心对称的超导体。在这里，我们报告发现在中心对称多频带超导体Ba的宽s波超导区域内具有明显的时间反转对称（BTRS）的\（s + is ^ {\ prime} \）超导相的狭窄圆顶的发现。_{1 −  x} K _x Fe ₂ As ₂（0.7  ≲  X  ≲  0.85）。我们使用μon自旋弛豫（μSR）技术观察该圆顶内部的自发磁场。此外，我们的详细比热研究表明，BTRS圆顶看起来非常接近费米表面拓扑的变化。以此，我们通过实验证明了由于电子系统拓扑变化而可能出现的新型量子态。