Devil's staircase structures in ${\phi }_0$ junction

Abstract

The superconductor-ferromagnet-superconductor ${\phi }_0$ junction provides a direct coupling between Josephson phase and magnetic moment of ferromagnetic barrier. We demonstrate an appearance of additional fractional subharmonic steps in the IV-characteristics of ${\phi }_0$ junction under external electromagnetic radiation due to spin-orbit coupling. An origin of subharmonic steps is related to the locking of magnetic moment precession to the Josephson oscillations. We prove that the positions of those steps follow a continued fraction algorithm.

13 pages, 7 figures