Superconducting Phase Transistor in Diffusive Four-terminal Ferromagnetic Josephson Junctions

TL;DR

This paper analyzes a four-terminal diffusive ferromagnetic Josephson junction, revealing how magnetic barriers and phase tuning can control supercurrent direction, enabling a potential nano-scale superconducting phase transistor.

Contribution

It provides an analytical framework for understanding supercurrent control in four-terminal magnetic Josephson junctions, introducing a novel phase transistor concept.

Findings

Magnetic barrier thickness can reverse supercurrent direction.

Supercurrent direction is tunable via superconducting phase differences.

The system can function as a nano-scale superconducting phase transistor.

Abstract

We study diffusive magnetic Josephson junctions with four superconducting terminals in the weak proximity limit where the leads are arranged in cross form. Employing the linearized Keldysh-Usadel technique, the anomalous Green's function and Josephson current are analytically obtained based on a quasiclassical theory using the Fourier series method. The derived results may be reduced to non-magnetic junctions by setting the exchange field equal to zero. We find that increments of the magnetic barrier thickness may cause a reversal of the supercurrent direction flowing into some of the leads, whereas the direction of current-flow remains invariant at the others. The reversal direction can be switched by tuning the perpendicular superconducting phases. In the non-magnetic case, we find that the supercurrent flowing between the leads in one direction can be tuned by changing the superconducting phase difference in the perpendicular direction. These findings suggest the possibility of constructing a nano-scale superconducting phase transistor whose core element consists of the proposed four-terminal Josephson junction with rich switching aspects.