Critical current of a S/F-I-N/S tunnel structure in a parallel magnetic field

TL;DR

This paper investigates how the critical current in a superconductor/ferromagnet-insulator-normal metal/superconductor tunnel structure varies with magnetic fields and orientations, revealing novel effects of spin splitting on superconductivity.

Contribution

It provides a microscopic analysis of the critical current behavior in S/F-I-N/S structures under magnetic fields, highlighting new effects due to spin splitting and phase state transitions.

Findings

Strong magnetism induces a pi/2 phase difference in the ground state.

External magnetic fields can reverse the critical current sign in parallel orientation.

The junction exhibits nonmonotonic current behavior with magnetic field changes.

Abstract

We study the critical current of a S/F-I-N/S tunnel structure - a proximity coupled superconductor (S) with thin ferromagnetic (F) and nonmagnetic (N) metals separated by an insulating (I) barrier - in an external magnetic field. The dependence of the current on exchange and external magnetic fields, and their mutual orientation is analyzed within the microscopic theory of the proximity effect. We find that the S/F-I-N/S contact with strong magnetism of the F layer is in a ground state with superconducting phase difference on the electrodes about pi/2. Low external magnetic field reverses the critical current sign of such a contact (a \pi-state of the junction) for parallel field orientation. For antiparallel alignment the dc Josephson current behavior is essentially nonmonotonic: by increasing an external magnetic field the current passes though a maximum, while the 0-phase state is held, and then the junction gets into the \pi-phase state with an opposite current direction. We demonstrate that the hybrid S/F-I-N/S metal structures possess new effects of the superconductivity in the presence of spin splitting, while an experimental set-up seems to be feasible and it may lead to further understanding of superconducting proximity effects in ferromagnetic materials.