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We present a mechanism for emission of electromagnetic terahertz waves by simulation. High Tc superconductors form naturally stacked Josephson junctions. When an external current and a magnetic field are applied to the sample, fluxon flow induces voltage. The voltage creates oscillating current through the Josephson effect and the current excites the Josephson plasma. The sample works as a cavity, and the input energy is stored in a form of standing wave of the Josephson plasma. A part of the energy is emitted as terahertz waves.PACS numbers: 74.50.+r, 74.25.Gz, 85.25.Cp Continuous coherent terahertz waves have various applications in scientific field such as biology and information science. One of the hurdles for technological advancements in the terahertz region of electromagnetic wave is the development of sources for intense and continuous coherent terahertz waves. Therefore, we investigate a new mechanism for emitting intense continuous and frequency tunable terahertz waves. In the high temperature superconductors, the strongly superconducting CuO 2 layers and insulating layers are alternatively stacked along the c-axis of the crystals and form a naturally multi-connected Josephson junction called intrinsic Josephson junction (IJJ). In the IJJ there appears a new excitation wave called Josephson plasma, the frequency of which is in the range of terahertz 1,2 . The frequency appears in the region inside the superconducting energy gap and the Landau damping is very weak, and thus the excited plasma decays by emitting a terahertz electromagnetic wave.For investigating an emission mechanism of terahertz electromagnetic wave from the IJJ, we use the following model shown by Figure 1. In Fig. 1 the IJJ is shown in green and the electrodes of a normal metal (for example gold) are shown in yellow. An external magnetic field B applied in the direction of the y-axis induces fluxons in the direction. The centers of fluxons are in the insulating layers. In this system, the superconducting and normal currents almost uniformly flow in the direction indicated by J in Fig.1. The fluxons flow in the direction of the x-axis with a velocity v and induce the flow voltage in the direction of the z-axis. These voltages creates the oscillating Josephson current along the z-axis by the Josephson effect, when temperature is low enough below T c and the superconducting current is smaller than the superconducting depairing current along the c-axis. This oscillating current interacts strongly with the Josephson plasma due to the nonlinear nature of the system and intensively excites the Josephson plasma wave as shown later. We use Bi 2 Sr 2 CaCu 2 O 8+δ that is appropriate in the experiments, and apply a magnetic field and external currents around J c the critical current to the IJJ. Then, the frequency of the plasma waves appears in the terahertz frequency range. The plasma wave is converted to an intense terahertz electromagnetic wave in the waveguide (dielectric) shown in orange in Fig. 1.In accordance with the mechanism mention...

Our new molecular dynamics (MD) simulation program, MODYLAS, is a general-purpose program appropriate for very large physical, chemical, and biological systems. It is equipped with most standard MD techniques. Long-range forces are evaluated rigorously by the fast multipole method (FMM) without using the fast Fourier transform (FFT). Several new methods have also been developed for extremely fine-grained parallelism of the MD calculation. The virtually buffering-free methods for communications and arithmetic operations, the minimal communication latency algorithm, and the parallel bucket-relay communication algorithm for the upper-level multipole moments in the FMM realize excellent scalability. The methods for blockwise arithmetic operations avoid data reload, attaining very small cache miss rates. Benchmark tests for MODYLAS using 65 536 nodes of the K-computer showed that the overall calculation time per MD step including communications is as short as about 5 ms for a 10 million-atom system; that is, 35 ns of simulation time can be computed per day. The program enables investigations of large-scale real systems such as viruses, liposomes, assemblies of proteins and micelles, and polymers.

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