Unconventional periodicities of the Little-Parks effect observed in a topological superconductor

The most distinctive feature of superconductivity is the presence of the complex-valued many-particle wave function that sustains phase coherence over macroscopic distances. One of its experimental manifestations is the fluxoid quantization in a superconducting ring. The single-value nature of the wave function dictates a universal phase change of 2π for any closed path around the ring. As a result, the fluxoid can only take on quantized values in integer steps of Φ₀=h/2e, where h is the Planck constant and the denominator of 2e is the signature of electron pairing, which is evidenced by a number of macroscopic quantum phenomena, such as the Little-Parks effect and the Josephson effect, where the critical temperature or the critical current oscillates with the periodicity of Φ₀ as has been observed in numerous polycrystalline and epitaixal rings of singlet superconductors of s-wave (e.g., Nb) and d-wave (e.g., cuprates). Here we report the observation of novel Little-Parks oscillation periodicities of 2Φ₀, 3Φ₀ and 4Φ₀, in addition to the conventional Φ₀, in mesoscopic rings of epitaxial β-Bi₂Pd, a topological triplet superconductor. These unexpected new findings suggest new physics to account for the novel quantizations.