Observation of Periodic pi-Phase Shifts in Ferromagnet-Superconductor Multilayers

TL;DR

This study demonstrates oscillatory critical temperature and current in Ni-Nb multilayers, providing evidence for periodic pi-phase shifts driven by ferromagnetic layer thickness variations.

Contribution

It presents experimental confirmation of pi-phase shifts in ferromagnet-superconductor multilayers through critical temperature and current measurements.

Findings

Oscillatory behavior of critical temperature and current with ferromagnetic layer thickness

Oscillation length matches magnetic length set by exchange field

Strong evidence for periodic pi-phase shifts in multilayers

Abstract

We report complementary studies of the critical temperature and the critical current in ferromagnet (Ni) - superconductor (Nb) multilayers. The observed oscillatory behavior of both quantities upon variation of the thickness of the ferromagnetic layer is found to be in good agreement with theory. The length scale of oscillations is identical for both quantities and is set by the magnetic length corresponding to an exchange field of 200 meV in Ni. The consistency between the behavior of the two quantities provides strong evidence for periodic pi- phase shifts in these devices.