Signatures of Majorana fermions in topological insulator Josephson junction devices

Abstract

We study theoretically the electrical current and low-frequency noise for a linear Josephson junction structure on a topological insulator, in which the superconductor forms a closed ring and currents are injected from normal regions inside and outside the ring. We find that this geometry offers a signature for the presence of gapless one-dimensional Majorana fermion modes that are predicted in the channel when the phase difference $\ensuremath{\varphi}$, controlled by the magnetic flux through the ring, is $\ensuremath{\pi}$. We show that for low temperature the linear conductance jumps when $\ensuremath{\varphi}$ passes through $\ensuremath{\pi}$, accompanied by nonlocal correlations between the currents from the inside and outside of the ring. We compute the dependence of these features on temperature, voltage, and linear dimensions, and discuss the implications for experiments.