Spontaneous supercurrent induced by ferromagnetic pi-junctions

TL;DR

This study demonstrates that ferromagnetic pi-junctions in superconducting loops induce spontaneous supercurrents, evidenced by asymmetric magnetization switching and half-integer flux quantization, revealing new quantum effects in mesoscopic superconducting systems.

Contribution

It provides experimental evidence of spontaneous supercurrents caused by ferromagnetic pi-junctions in superconducting loops, a novel observation in mesoscopic physics.

Findings

Asymmetric magnetization switching observed

Spontaneous currents detected near zero field

Half-integer flux quantization at low temperatures

Abstract

We present magnetization measurements of mesoscopic superconducting niobium loops containing a ferromagnetic (PdNi) pi-junction. The loops are prepared on top of the active area of a micro Hall-sensor based on high mobility GaAs/AlGaAs heterostructures. We observe asymmetric switching of the loop between different magnetization states when reversing the sweep direction of the magnetic field. This provides evidence for a spontaneous current induced by the intrinsic phase shift of the pi-junction. In addition, the presence of the spontaneous current near zero applied field is directly revealed by an increase of the magnetic moment with decreasing temperature, which results in half integer flux quantization in the loop at low temperatures.