Zero-bias peaks at zero magnetic field in ferromagnetic hybrid nanowires

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, Vaitiekėnas et al. show that zero-bias peaks—potential Majorana bound states—can be induced without an external magnetic field.