Dissipative-free chiral edge transport in stacked (Al/Ni)₁₀ multilayers

Using the phase-sensitive Josephson interferometry technique, we demonstrate signatures of non-trivial edge modes in stacked multilayers S(NF)₁₀NI(NF)₁₀NS formed by conventional normal (N = Al) and magnetic (F = Ni) nanometer-thick metallic films, an insulating interlayer (I = Al oxide), and two superconducting (S = Nb) electrodes. The main findings are (i) strongly upwardly shifted periodic SQUID-like dependences of the maximum supercurrent on the probing in-plane magnetic field instead of conventional Fraunhofer patterns with nodes and (ii) h/e period of the oscillations rather than the superconducting h/2e flux quanta. Replacing the I layer with a S′IS′ junction (S′ is an ultrathin Nb layer) led to the restoration of Fraunhofer behavior, indicating the transformation of supercurrent into hybrid electron-hole modes upon contact of the superconducting S′ plane with an (NF)₁₀N multilayer. Analyzing the data obtained, we come to the conclusion that the (NF)₁₀N multilayers under study are three-dimensional electronic systems, possessing gapped bulk and side surface states with quasi-one-dimensional backscatter-free in-gap hinge modes propagating unidirectionally and possibly topologically protected. Two probable origins of the observed phenomena are discussed - a fully quantum scenario and that based on non-Hermitian physics in non-conservative systems.