Computer simulation on terahertz emission from intrinsic Josephson junctions of high-$T_c$ superconductors

Solving coupled nonlinear sine-Gordon equations and Maxwell equations numerically, we study the electromagnetic and superconducting properties of the single crystal of high-$T_c$ superconductor ${\mathrm{Bi}}_2{\mathrm{Sr}}_2\mathrm{Ca}{\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$ with a static magnetic field applied parallel to the $ab$ plane and a dc fed in along the $c$ axis. Cavity resonances of transverse plasma occur in the intrinsic Josephson junctions with frequencies in terahertz regime. It is revealed that the electromagnetic wave can transmit from the junctions into space. The emitted energy counted by the Poynting vector is about $400\mathrm{W}∕{\mathrm{cm}}^2$. The frequency as well as the energy of emission can be tuned almost continuously by the current and magnetic field.

Figure 1

(Color online) Schematic diagram of the emitter of terahertz electromagnetic wave. The intrinsic Josephson junctions are sandwiched by two gold electrodes through which a dc bias is fed into the system.

Figure 2

Radiation power counted by the Poynting vector as a function of the voltage across the stack of IJJs. The external current corresponds to the b peak is $J_{\mathrm{ext}}=1.33J_c$. The inset is the enlarged view of the main panel in the region $V<235\mathrm{mV}$.

Figure 3

(Color online) Frequency spectra for the voltage at the main peaks in Fig. 2.

Figure 4

(Color online) Left panel: snapshots for the magnetic and electric fields at the largest resonance in Fig. 2, where the static backgrounds have been subtracted. Right panel: snapshot of vortex configuration.

Figure 5

(Color online) Radiation power at different applied magnetic fields in units of Tesla as a function of the voltage across the stack of IJJs. The frequency in the upper axis is determined by the ac Josephson relation.