The ac Driven Annular Josephson Junctions: The Missing Steps

TL;DR

This paper investigates how external radiation influences the locking behavior of underdamped annular Josephson junctions, revealing that the presence and type of flux excitations determine the appearance of Shapiro steps.

Contribution

It demonstrates that the type and coexistence of flux excitations in Josephson junctions critically affect their response to external radiation, clarifying conditions for observing Shapiro steps.

Findings

Shapiro steps occur only with trapped fluxons or fluxon-antifluxon pairs.

Simultaneous circulation of fluxons and antifluxons suppresses Shapiro steps.

The ability to lock with external radiation depends on flux excitation types.

Abstract

Examination of an annular system of underdamped Josephson junctions in the presence of external radiation showed that the ability of the system to lock with some external radiation was determined not only by the number but also by the type of rotating excitations (fluxons or antifluxons). Shapiro steps can be observed in the current-voltage characteristics only in the system with trapped fluxons or in the system with fluxon-antifluxon pairs. If the trapped fluxons circulate simultaneously with fluxon-antifluxon pairs, there are no Shapiro steps regardless of the amplitude or frequency of the applied external radiation.