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Two superconducting banks are connected by a bridge of magnetic material. Inside the bridge lies a domain wall: a narrow boundary where the magnetization rotates, like a column of soldiers changing their marching direction. The current flowing through such a bridge behaves not like a calm river but like a stream bending around an obstacle: it curls into loops and changes its strength.

The authors calculated that shifting the wall along the track, even by fractions of a micron, noticeably changes the critical current. At certain positions, the current transitions from the ordinary mode to a 'flipped' one, where the superconducting phase shifts by half a period. Such sensitivity turns the domain wall into a control knob: no external magnets or additional contacts are needed.

This matters for racetrack memory: domain walls already store bits, and now they can also be read by the same current that moves the data. The device becomes simpler and more compact — one and the same path serves as both carrier and detector.

Original abstract

as written by the authors arXiv:2604.12742

We investigate the Josephson coupling between two superconducting electrodes connected by a ferromagnetic racetrack hosting a Bloch-like domain wall (DW). We show that the interplay between superconductivity and the DW leads to highly non-trivial spatial distributions of the supercurrent, including the formation of current loops and a strong sensitivity to the DW position and orientation. We further demonstrate that the Josephson critical current $$I_c$$ can be efficiently controlled by the DW position along the racetrack, exhibiting pronounced variations and tunable $$0$$--$$\pi$$ transitions. These results provide clear design principles for superconducting racetrack devices and establish domain walls as a viable control element for readout schemes in racetrack memory architectures.