Numerical studies on the collective vortex flow and RF responses of the intrinsic Josephson junction with periodic potentials

Abstract

In-phase collective motion of Josephson vortices (JVs) over the junctions stack as well as the strong interaction between the vortices and the electromagnetic modes are needed to realize effective electromagnetic (EM) wave radiations from the intrinsic Josephson junction stacks. We have been studied the interaction from the RF responses of the intrinsic Josephson junctions in the flux-flow states. So far, the Shapiro-step-like responses were found in the flux-flow state with a cooperation of pancake vortices introduced by tilting the magnetic field direction out from the ab plane. The Shapiro-step-like responses suggest that the JVs collectively move keeping the rectangular lattice. We have proposed that the pancake vortices develop a periodic pinning potential that stabilizes the in-phase collective motion of JVs. We have carried out numerical simulations based on the coupled sine-Gordon equation considering the effect of the periodic pinning potential on the vortex dynamics. Current-voltage (I-V) properties of the inductively-coupled Josephson junction stack, which represent the intrinsic Josephson junction stack, were numerically obtained for both static and flux-flow states. It is shown that the periodic pinning potentials of appropriate strengths revealed Shapiro-step-like responses on the I-V properties of flux-flow states. It is also shown that the periodic pinning potentials stabilize the in-phase collective motion of the JVs over the junction stacks.