High-T_c cuprate superconductors have several special properties; higher superconducting transition temperature and unconventional Cooper pairing. Additionally, in these materials, superconducting layers and insulating layers are piled up alternately, and thus Josephson junctions between layers are formed spontaneously. These junctions are called the intrinsic Josephson junctions.

If a voltage is applied to the Josephson junctions, an ac current flows by the Josephson effect. Because of this ac current, an electromagnetic (EM) wave is emitted from junctions, and frequency of this wave reaches to the THz regime.

In this study, we focus on synchronization phenomenon of EM fields in the junctions. We use the numerical model of intrinsic Josephson junction proposed by Koyama and Tachiki [1] and we investigate how EM fields will synchronize in the junctions by simulating the EM fields and phase differences of order parameters between neighboring superconducting layers in the junctions, especially, transient state before coherent motions of EM fields, numerically, using the finite element method [2]. In Fig.1, we show an example of EM fields in the transient state.

Fig.1 Distributions of B_xin center of the junctions at t=2.0×10^-12 sec((a)) and t=20.0×10^-11 sec((b)). Distributions of B_yin center of the junctions at t=2.0×10^-12 sec((c)) and t=20.0×10^-11 sec((d)).

 [1] Koyama T and Tachiki M 1996 Phys. Rev. B 54 16183 (1996)
[2] Fujiki F and Kato M, J.Phys. Conf. Ser. 1590 012018 (2020)

Keywords: Intrinsic Josephson junction, THz, Synchronization phenomenon, Finite Element Method