Electrical manipulation of Majorana Fermions in an interdigitated superconductor-ferromagnet device*

We show that a topological phase supporting Majorana fermions can form in a 2DEG adjacent to an interdigitated superconductor-ferromagnet structure. An advantage of this setup is that the 2DEG can inherit the required Zeeman splitting and superconductivity from a single interface, allowing one to utilize a wide class of 2DEG's including the surface states of bulk InAs. We demonstrate that the interdigitated device supports a robust topological phase when the finger spacing $\lambda$ is smaller than the Fermi wavelength $\lambda_F$. In this regime the electrons effectively see a ``smeared" Zeeman splitting and pairing field despite the interdigitation. The topological phase survives even in the opposite limit $\lambda<\lambda_F$, though with a reduced bulk gap. We also describe how to electrically generate a vortex in this setup to trap a Majorana mode, which can be detected through edge tunneling spectroscopy.