Semiconductor-ferromagnet-superconductor planar heterostructures for 1D topological superconductivity

Abstract

Hybrid structures of semiconducting (SM) nanowires, epitaxially grown superconductors (SC), and ferromagnetic-insulator (FI) layers have been explored experimentally and theoretically as alternative platforms for topological superconductivity at zero magnetic field. Here, we analyze a tripartite SM/FI/SC heterostructure but realized in a planar stacking geometry, where the thin FI layer acts as a spin-polarized tunneling barrier between the SM and the SC. We optimize the system's geometrical parameters using microscopic simulations, finding the range of FI thicknesses for which the hybrid system can be tuned into the topological regime. Within this range, and thanks to the vertical confinement provided by the stacking geometry, trivial and topological phases alternate regularly as the external gate is varied, displaying a hard topological gap that can reach half of the SC one. This is a significant improvement compared to setups using hexagonal nanowires, which show erratic topological regions with typically smaller and softer gaps. Our proposal provides a magnetic field-free planar design for quasi-one-dimensional topological superconductivity with attractive properties for experimental control and scalability.

Conductance Spectroscopy of Majorana Zero Modes in Superconductor-Magnetic Insulating Nanowire Hybrid Systems

“…With the aforementioned on one hand, the basic Rashba wire setup has further drawbacks which includes the requirement of large magnetic fields that could potentially destroy superconductivity [37][38][39][40] apart from the practicalities of precise magnetic field alignment [41]. Recently, efforts are being made towards realizing * bm@ee.iitb.ac.in topological superconductivity with zero external magnetic fields by using proximity effects from magnetic insulators (MI) [42][43][44][45][46][47][48][49][50][51][52]. Recent experimental [43] and theoretical works [44][45][46][47][48]51] featuring this setup indicate that at very low external magnetic fields, or even zero external magnetic fields, a topological MZM phase can emerge.…”

Conductance spectroscopy of Majorana zero modes in superconductor-magnetic insulator nanowire hybrid systems

“…With the aforementioned on one hand, the basic Rashba wire setup itself has further drawbacks which includes the requirement of large magnetic fields that could potentially destroy superconductivity [41][42][43][44] apart from the practicalities of precise magnetic field alignment 45 . Recently, efforts are being made towards realizing topological superconductivity with zero external magnetic fields by using proximity effects from magnetic insulators (MI) [46][47][48][49][50][51][52][53][54][55][56][57][58][59] . Recent experimental 47 and theoretical works [48][49][50][51][52]55,60 featuring this setup indicate that at very low external magnetic fields, or even zero external magnetic fields, a topological phase can emerge.…”