Realizing Majorana zero mode with a stripe of \emph{ionized} and \emph{isolated} magnetic atoms on a \emph{layered} superconductor

TL;DR

This paper proposes device designs using isolated magnetic atoms or ions on layered superconductors to realize Majorana zero modes with significantly reduced magnetic exchange coupling requirements.

Contribution

It introduces novel device configurations with isolated magnetic atoms or ions on layered superconductors that enable Majorana zero modes at weak coupling.

Findings

Spontaneous spiral magnetic order forms in proposed devices.

Majorana zero modes appear at the ends of the wire.

Topological superconductor gap exceeds half of the parent superconductor's gap.

Abstract

It has been proposed that a line junction between spiral magnet and superconductor or between ferromagnet and superconductor with Rashba spin-orbital coupling can produce Majorana zero mode (MZM) at the ends of the line. However, a strong magnetic exchange coupling between the magnetic atoms and the superconductor (about half of the bandwidth of the superconductor) is needed to obtain MZM. Here, we design devices to reduce the needed magnetic exchange coupling. In the first proposal, we cover a very narrow $s$-wave superconducting wire formed by a monolayer film or a layered material (such as FeSe or FeSe monolayer on SrTiO$_3$) with \emph{isolated} magnetic atoms. In our second proposal, we place a line of \emph{isolated} magnetic \emph{ions} on a monolayer superconductor or a \emph{layered} superconductor (such as FeSe). We show that, in the above devices, a spiral magnetic order will develop spontaneously to produce a 1D $p$-wave topological superconductor with a sizable gap (above 1/2 of the parent superconducting gap), even for a weak magnetic exchange coupling (less than 1/10 of the bandwidth). The topological superconductor has MZM at ends of the wire.