Devil's staircases in the IV characteristics of superconductor/ferromagnet/superconductor Josephson junctions

Abstract

We study the effect of coupling between the superconducting current and magnetization in the superconductor/ferromagnet/superconductor Josephson junction under an applied circularly polarized magnetic field. Manifestation of ferromagnetic resonance in the frequency dependence of the amplitude of the magnetization and the average critical current density is demonstrated. The IV characteristics show subharmonic steps that form devil's staircases, following a continued fraction algorithm. The origin of the found steps is related to the effect of the magnetization dynamics on the phase difference in the Josephson junction. The dynamics of our system is described by a generalized RCSJ model coupled to the Landau-Lifshitz-Gilbert equation. We justify analytically the appearance of the fractional steps in IV characteristics of the superconductor/ferromagnet/superconductor Josephson junction.

Microwave induced tunable subharmonic steps in superconductor–ferromagnet–superconductor Josephson junction

“…In case of external electromagnetic field which leads to the additional electric current I ac = A sin Ωt, the width of the Shapiro step is proportional to ∝ J n (A/Ω), where J n is the Bessel function of first kind. The preliminary results (not presented here) show that the width of the Shapiro-like steps under external magnetic field has a more complex frequency dependence 20 . This question will be discussed in detail somewhere else.…”

“…In Ref. [20] we show that taking into account the effective field due to Josepshon energy and at FMR, additional subharmonic current steps appear in the IV-characteristic for overdamped SFS junction with spin wave excitations (magnons). It is found that the position of the current steps in the IV-characteristics form devil's staircase structure which follows continued fraction formula 20 .…”

Критический Ток В Длинном Джозефсоновском Контакте Во Внешнем Магнитном Поле При Слабом Пиннинге

“…В этой модели расчеты могут быть выполнены весьма точно, что позволяет разобраться в деталях происходящих процессов. Поэтому процессы в длинных джозефсоновских контактах анализируются в значительном числе работ [7][8][9].…”

Критический Ток В Длинном Джозефсоновском Контакте Во Внешнем Магнитном Поле При Сильном Пиннинге

“…Она может быть решена весьма точно, что позволяет понять различные детали происходящих процессов. Поэтому исследованиям процессов в длинных джозефсоновских контактах посвящено значительное число работ [7][8][9].…”