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At high enough input power in stacks of Bi2Sr2CaCu2O8 intrinsic Josephson junctions a hot spot (a region heated to above the superconducting transition temperature) coexists with regions still in the superconducting state. In the "cold" regions cavity resonances can occur, synchronizing the ac Josephson currents and giving rise to strong coherent THz emission. We investigate the interplay of hot spots and standing electromagnetic waves by low temperature scanning laser microscopy and THz emission measurements, using stacks of various geometries. For a rectangular and a arrowshaped structure we show that the standing wave can be turned on and off in various regions of the stack structure, depending on the hot spot position. We also report on standing wave and hot spot formation in a disk shaped mesa structure.

We demonstrate experimentally the existence of Josephson junctions having a doubly degenerate ground state with an average Josephson phase ψ=±φ. The value of φ can be chosen by design in the interval 0<φ<π. The junctions used in our experiments are fabricated as 0-π Josephson junctions of moderate normalized length with asymmetric 0 and π regions. We show that (a) these φ Josephson junctions have two critical currents, corresponding to the escape of the phase ψ from -φ and +φ states, (b) the phase ψ can be set to a particular state by tuning an external magnetic field, or (c) by using a proper bias current sweep sequence. The experimental observations are in agreement with previous theoretical predictions.

We study an interesting state with a self-generated magnetic flux in a long Josephson junction. The critical current density j c is assumed to alternate randomly along the tunnel contact on a length scale much less than the local Josephson penetration depth. The phase difference is then a sum of an alternating term and a smooth term which self-consistently contribute to the formation of a stationary state with self-generated flux. Two types of Josephson vortices are found in this state, one with magnetic flux ⌽ 1 Ͻ⌽ 0 /2 and another one with magnetic flux ⌽ 2 ϭ⌽ 0 Ϫ⌽ 1 Ͼ⌽ 0 /2. ͓S0163-1829͑98͒50306-2͔