In-phase electrodynamics and terahertz wave emission in extended intrinsic Josephson junctions

Abstract

Strong emission of subterahertz electromagnetic (EM) waves has been observed recently in the high ${T}_{c}$ superconductor ${\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8}$ intrinsic Josephson junctions (IJJ's). We investigate numerically the dynamics of the EM fields both inside and outside the IJJ's emitting terahertz EM waves under a constant bias current, using two-dimensional models composed of IJJ's and the space surrounding them: (1) $xy$ model and (2) $xz$ model. In the $xy$ model we investigate the EM modes excited in the rectangular junctions. In the voltage state the Josephson oscillation generates the oscillating EM field having nodes inside the junctions. The number of nodes depends on the DC voltage appearing in the junctions, and their direction is parallel to the shorter side of the junctions. The EM field shows a complex distribution pattern in the near field region. In the region far from the junctions we have only the expanding EM wave oscillating with the Josephson frequency. In the $xz$ model we study the EM waves emitted in the $xz$ plane from the junctions covered with normal electrodes. It is shown that the power of the emitted EM waves has distribution similar to that in the dipole emission in the system where electrodes of the same size are attached on top and bottom junctions. In the asymmetric system where the lower electrode is larger than the upper one the power distribution of emitted EM wave deviates from that in the dipole emission.