Fractional Little-Parks effect observed in a topological superconductor

TL;DR

This paper reports the observation of fractional Little-Parks oscillations in a topological superconductor, indicating the presence of quasiparticles with fractional effective charges and suggesting Majorana edge states.

Contribution

First observation of fractional Little-Parks effect in a topological superconductor, linking it to fractional Josephson effect and Majorana states.

Findings

Observation of oscillations at 2, 3, and 4 times the flux quantum

Evidence of quasiparticles with fractional charges

Potential link to chiral Majorana edge states

Abstract

In superconductors, the condensation of Cooper pairs gives rise to fluxoid quantization in discrete units of $\Phi_0 = hc / 2e$. 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 $\Phi_0$. Here we report the observation of fractional Little-Parks effect in mesoscopic rings of epitaxial $\beta$-Bi$_2$Pd, a topological superconductor. Besides $\Phi_0$, novel Little-Parks oscillation periodicities of $2\Phi_0$, $3\Phi_0$ and $4\Phi_0$ 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.