Resonant electromagnetic emission from intrinsic Josephson-junction stacks with laterally modulated Josephson critical current

Intrinsic Josephson-junction stacks realized in mesas fabricated out of high-temperature superconductors may be used as sources of coherent electromagnetic radiation in the terahertz range. The major challenge is to synchronize Josephson oscillations in all junctions in the stack to get significant radiation out of the crystal edge parallel to the c axis. We suggest a simple way to solve this problem via artificially prepared lateral modulation of the Josephson critical current identical in all junctions. In such a stack, phase oscillations excite the in-phase Fiske mode when the Josephson frequency matches the Fiske-resonance frequency which is set by the stack lateral size. The powerful, almost standing electromagnetic wave is excited inside the crystal in the resonance. This wave is homogeneous across the layers, meaning that the oscillations are synchronized in all junctions in the stack. We evaluate behavior of the I-V characteristics and radiated power near the resonance for arbitrary modulation and find exact solutions for several special cases corresponding to symmetric and asymmetric modulations of the critical current.