Multi-scale simulation for terahertz wave emission from the intrinsic Josephson junctions

Abstract

A numerical method applicable to the analysis of the multi-scale electromagnetic(EM) excitations in intrinsic Josephson junctions (IJJs) is presented. Usingthis method, we investigate the EM wave emission from the IJJs observed inBi2Sr2CaCu2O8 mesas. The IJJs have three length scales that are greatly differentin magnitude, i.e. the distance between superconducting layers (d ∼ 10 − 3 µm), the Josephsonlength (λJ ∼ 1 µm) and thec-axis penetrationdepth (λc ∼ 102 µm). The EM field excited in the IJJs generally shows spatial variation of these three lengthscales at the same time. In our numerical method the coupled dynamical equations forthe phase differences and the EM field can be solved simultaneously in all thescales in the whole space composed of the IJJs and the surrounding vacuum. Weclarify that the spatial symmetry of the EM field excited at the resonance with theπ-cavity-mode is differentfrom that with the 2π-cavity-mode. The strong EM wave emission originating from theπ-cavity-mode resonance takes place in the region where the uniform branch becomes unstable in theI–V characteristics.