Emission of terahertz electromagnetic waves from intrinsic Josephson junction arrays embedded in resonance LCR circuits

The emission of terahertz electromagnetic waves from an intrinsic Josephson junction array (IJJA) embedded in an LCR resonant circuit is studied theoretically. A bias current is applied to the electrodes at the top and bottom of the array. In the voltage state, the ac Josephson current generates a displacement current in the IJJA, and both the currents induce an oscillating current in the electrodes. We describe the whole system, including the array and the environment around it, in terms of an LCR resonant circuit. When the Josephson frequency is in the resonance frequency region of the LCR circuit, the amplitudes of the displacement current in the Josephson junction array and the oscillating current in the electrodes both are strongly enhanced by a feedback process. We calculate the emission power and the current-voltage (I-V) characteristic curve for the system. Inside the frequency region of the LCR circuit resonance, stable and intense emission occurs in both the increasing and decreasing processes of the high-bias current. In the emission region the I-V characteristic curve has a dip structure. These results are consistent with those of the emission observed in a high-bias current region by using mesa-shaped samples of Bi₂Sr₂CaCu₂O _8+δ. We also discuss the difference between the properties of the emission and the I-V characteristic curve for intrinsic Josephson junctions embedded in and shunted by the LCR resonant circuit.