Observation of the crossover from quantum fluxoid to half-quantum fluxoid in a chiral superconducting device.

Topological superconductors are one of the intriguing material groups from the viewpoint of not only condensed matter physics but also industrial applications such as quantum computers based on Majorana fermion. For real applications, developments of thin-film topological superconductors are highly desirable. Bi/Ni bilayer is a possible candidate for thin-film chiral superconductors where the time-reversal symmetry is broken. Here we report the phase shift of resistance oscillations by half flux quantum in a ring-shaped device of epitaxial Bi/Ni bilayer induced by a small magnetic field through the ring. The half quantum fluxoid can be decisive evidence for unconventional superconductors where the superconducting order parameter has an internal degree of freedom. The present result provides a functional operating principle for quantum devices where the phase of the supercurrent can be shifted by [Formula: see text] with a small magnetic field, based on the internal degree of freedom had by topological superconductivity.