Interaction of hot spots and terahertz waves inBi2Sr2CaCu2O8intrinsic Josephson junction stacks of

Abstract

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.

Three-dimensional numerical analysis of terahertz radiation emitted from intrinsic Josephson junctions with hot spots

“…The appearance of such hot spots whose positions are asymmetric with respect to the center of the mesas have been already reported in previous experimental studies. [20][21][22] …”

“…Moreover, the radiation patterns emitted by inhomogeneous samples have not been investigated in previous studies. Recently, Wang et al have reported the appearance of hot spots where the temperature is locally high, [20][21][22] and these inhomogeneities are considered to affect the emission from the IJJs.…”

The influence of standing waves on synchronization and self-heating of Josephson junctions in resonant systems

“…Due to strong extraction of Joule heat (the self-heating) the temperature of junctions in the center of the line can exceed the temperature at ends as much as 1.5 times that can lead to the formation of the "hot spot" in the center of the line, whereas at the same time junctions at ends of the line radiate coherently. Thus, we showed that three particularities noted in experiments [2][3][4][6][7][8], namely the self-induced resonant steps on I-V characteristics, strong coherent emission at these steps and the appearance of "hot spots" have the same origin that is the resonance behavior of the system at certain bias currents. …”

“…The detail calculations can be made with the use of the proposed model. Note that for the description of the experiments [2][3][4][6][7][8] with the given width of the sample it is necessary to calculate distributions of voltages and currents also along the y-axis.…”

“…To explain the effect, the hypothesis of the nonuniform distribution of critical currents of intrinsic junctions was proposed [2] as well as the hypothesis about the existence of the plasma resonance in the system [5]. Experiments showed also that the temperature along the measured samples of intrinsic Josephson junctions can be strongly inhomogeneous [6] and the so-called "hot spots" (i.e., places in the sample where the temperature can even reach the critical temperature of the superconductor) can be formed [7,8].…”