ABSTRACT
Continuous, coherent subterahertz radiation arises when a dc voltage is applied across a stack of the many intrinsic Josephson junctions in a Bi2Sr2CaCu2O(8+δ) single crystal. The active junctions produce an equal number of I-V characteristic branches. Each branch radiates at a slightly tunable frequency obeying the Josephson relation. The overall output is broadly tunable and nearly independent of heating effects and internal cavity frequencies. Amplification by a surrounding external cavity to allow for the development of a useful high-power source is proposed.
ABSTRACT
Subterahertz radiation emitted from a variety of short rectangular-, square-, and disk-shaped mesas of intrinsic Josephson junctions fabricated from a Bi(2)Sr(2)CaCu(2)O(8+δ) single crystal was studied from the observed I-V characteristics, far-infrared spectra, and spatial radiation patterns. In all cases, the radiation frequency satisfies the conditions both for the ac Josephson effect and for a mesa cavity resonance mode. The integer higher harmonics observed in all spectra imply that the ac Josephson effect plays the dominant role in the novel dual-source radiation mechanism.
ABSTRACT
Using a 3D parallelepiped model of the stack of intrinsic Josephson junctions, we calculate the cavity resonance modes of Josephson plasma waves excited by external electric currents. The cavity modes accompanied by static phase kinks of the order parameter have been intensively investigated. Our calculation shows that the kink phase state is unfavorable, since the static phase kinks reduce the order parameter amplitude and thus the superconducting condensation energy. We point out that the oscillating magnetic field of the cavity mode penetrates the vacuum from the sample surfaces and the energy of the magnetic field plays an important role to determine the orientation of the cavity resonance mode. On the basis of the above discussions, we calculate the I-V characteristic curve, the THz wave emission intensity and the other physical quantities.
