Hybrid quantum materials allow for quantum phases that otherwise do not exist in nature(1,2). For example, a one-dimensional topological superconductor with Majorana states bound to its ends can be realized by coupling a semiconductor nanowire to a superconductor in the presence of a strong magnetic field(3-5). However, the applied magnetic fields are detrimental to superconductivity, and constrain device layout, components, materials, fabrication and operation(6). Early on, an alternative source of Zeeman coupling that circumvents these constraints-using a ferromagnetic insulator instead of an applied field-was proposed theoretically(7). Here, we report transport measurements in hybrid nanowires using epitaxial layers of superconducting Al and the ferromagnetic insulator EuS on semiconducting InAs nanowires. We infer a remanent effective Zeeman field exceeding 1 T and observe stable zero-bias conductance peaks in bias spectroscopy at zero applied field, consistent with topological superconductivity. Hysteretic spectral features in applied magnetic field support this picture.

By incorporating a ferromagnetic layer in their superconductor-semiconductor nanowire hybrid device, Vaitiekenas et al. show that zero-bias peaks-potential Majorana bound states-can be induced without an external magnetic field.