Fractional Little-Parks effect observed in a topological superconductor

Abstract

In superconductors, the condensation of Cooper pairs gives rise to fluxoid quantization in discrete units of Φ 0 = hc 2e. 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 in the period of Φ 0 . Here we report the observation of fractional Little-Parks effect in mesoscopic rings of epitaxial β-Bi 2 Pd, a topological superconductor.Besides Φ 0 , novel Little-Parks oscillation periodicities of 2Φ 0 , 3Φ 0 and 4Φ 0 are also observed, implying quasiparticles with effective charges being a fraction of a Cooper pair. We show that the fractional Little-Parks effect may be closely related to the fractional Josephson effect, which is a key signature of chiral Majorana edge states.