Electromagnetic wave emission from intrinsic Josephson junction stacks; A Review of theory and simulation

高温超伝導体固有ジョセフソン接合からの電磁波発振; 理論及びシミュレーション研究概説

町田 昌彦  ; 太田 幸宏*; 小山 富男*; 松本 秀樹*

Machida, Masahiko; Ota, Yukihiro*; Koyama, Tomio*; Matsumoto, Hideki*

高温超伝導体の産業応用としてジョセフソン接合を利用したテラヘルツ帯の電磁波レーザー発振が提案されている。本発表では、このテラヘルツの電磁波発振についてこれまでの理論的研究や数値的研究をレビューし、今後の動向について講演を行う。講演では、まず、テラヘルツ帯の電磁波がさまざまな科学技術分野で必要とされておりその発振源の開発がいかに重要であるかについて議論し、高温超伝導体を利用したテラヘルツ発振研究の歴史(特に理論や数値シミュレーション研究)をレビューし、何が判明した一方、何が課題として残されているかを明らかにする。その課題提起を受け、講演者らの研究開発の取り組みを手短に紹介し、今後の理論そして分野全体の動向についてコメントする。

Since the discovery of intrinsic Josephson effects in High-Tc cuprate superconductors, a tremendous number of theoretical and experimental studies have been made to clarify the coupling nature between stacked junctions. The reason comes from an expectation that Josephson junctions stacked in atomic-scale synchronize and high-power electromagnetic wave radiates. Consequently, two types of couplings, called "inductive and capacitive couplings" have been so far established. On the basis of the inductive coupling, several papers suggested that THz high-power emission is possible by using Josephson vortex flow states in the presence of layer parallel magnetic field and c-axis transport current. However, there has been no clear evidence of the emission in vortex flow states, although a few works found out only the sign. Afterwards, Ozyuzer et al., reported that they successfully observe a clear emission from intrinsic Josephson junctions. The situation was rather an unexpected one, since the magnetic field is not applied and the employed size is much larger than the experimental trends at that time. In this presentation, we review a history of the quest of the high power electromagnetic wave emission from intrinsic Josephson stacks before and after the Ozyuzer's work from a theoretical and numerical view. Especially, we would like to emphasize that direct numerical simulation techniques on multi-scale dynamical problems between inside and outside the junction have fully developed by authors.