Emission of continuous coherent terahertz waves with tunable frequency by intrinsic Josephson junctions

Abstract

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...

Radiation from Flux Flow in Josephson Junction Structures

“…Away from resonances and for resonances limited by quasiparticle damping P rad ∝ N 2 . For BSCCO crystals at ω/2π = 1 THz, we obtain P rad /w ≈ 24 mW/cm, while for It is interesting to compare our estimate with recent large-scale simulations of THz radiation out of BSCCO mesa by Tachiki et al [27]. They solve the Maxwell equations coupled with the equations for the intralayer phases inside the crystal and the dielectric media.…”

“…What is more, there are many junctions on the scale of the radiation wavelength, and so they will super-radiate when synchronized. Due to these advantages, the moving Josephson vortex lattice in layered superconductors was proposed as a source of monochromatic tunable continuous electromagnetic radiation in the terahertz frequency range [24,25,26,27,28]. Experimentally, radiation from the high-temperature layered superconductor BSCCO at relatively low frequencies, 7-16 GHz, was detected by Hechtfischer et al [29].…”

Mechanism of Terahertz Electromagnetic Wave Emission from Intrinsic Josephson Junctions

“…The emission frequencies are inversely proportional to the length of the shorter side of the samples in agreement with experiments. Emission of terahertz electromagnetic (EM) waves from intrinsic Josephson junctions (IJJ) in high temperature superconductors has been extensively studied [1,2,3,4,5,6,7,8]. Recently, Ozyuzer et al succeeded in detecting strong and continuous emission of terahertz EM waves from mesa-shaped samples of the high temperature superconductor Bi 2 Sr 2 CaCu 2 O 8 (BSCCO) [9].…”

Radiation due to Josephson Oscillations in Layered Superconductors

“…Layered high-temperature superconductors like Bi 2 Sr 2 CaCu 2 O 8 (BSCCO) offer a very attractive alternative for developing radiation sources. [6,7,8,9] A large value of the gap (up to 60 meV) allows for very high Josephson frequencies, which can be brought into the practically important terahertz range. Moreover, intrinsic JJs (IJJS) have much closer parameters than artificial ones as these parameters are controlled by the atomic crystal structure rather than by amorphous dielectric layer in artificial JJs.…”

“…[6,7,8,9] The inductive interlayer coupling typically promotes formation of the triangular vortex lattice. However, to generate noticeable outside radiation oscillations induced by the moving lattice have to be in phase in different layers, which is realized only if the moving vortices form a rectangular lattice.…”