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 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.

Exceptional degeneracies in non-Hermitian Rashba semiconductors

“…We also note that there is reasonable evidence suggesting that the system studied here as well as the main findings are within experimental reach. In fact, very similar systems as studied here have already been fabricated, including semiconductors with SOC made of InAs [72][73][74][75][76][77] or InSb [78][79][80][81][82] and ferromagnets producing sizeable Zeeman fields [83][84][85][86][87][88][89]. The coupling between ferromagnet and semiconductor, here characterized by Γ σ , can be controlled by an appropriate manipulation of both the spin-dependent density of states in the lead and the tunneling between lead and semiconductor.…”

Nonsinusoidal current-phase relations in semiconductor-superconductor-ferromagnetic insulator devices

“…Therefore, ferromagnetic hybrid junctions allow exploring the parameter space beyond the conventional regime (µ ∆ > |h|). Note that we do not refer to a particular arrangement of the layers in the lateral region, as different combinations of interfaces, for instance, tripartite arrangement [58,59] and tunneling arrangement [60,61], allows induction of both superconducting pairing and exchange field in the semiconductor.…”

“…The magnitude of the h field can also vary due to a nonuniform coupling strength. Moreover, recent theoretical investigations of ferromagnetic InAs-Al-EuS nanowires showed that the electrostatic environment is crucial in modulating the effect of the EuS on the InAs [58,59,61], suggesting that, in principle, it is possible to tune the induced exchange field electrostatically.…”

Direct observation of a superconducting vortex diode

“…In recent years, a significant theoretical and experimental effort has been directed toward the interplay between magnetism and superconductivity [1][2][3][4][5][6][7][8][9][10][11][12][13] . Incorporating spin-orbit coupling (SOC) and considering the presence of a magnetic exchange field can theoretically predict the emergence of a nonreciprocal critical current 14 .…”