Coherent Terahertz Emission of Intrinsic Josephson Junction Stacks in the Hot Spot Regime

Abstract

We report on THz emission measurements and low temperature scanning laser imaging of Bi2Sr2CaCu2O8 intrinsic Josephson junction stacks. Coherent emission is observed at large dc input power, where a hot spot and a standing wave, formed in the "cold" part of the stack, coexist. By changing bias current and bath temperature, the emission frequency can be varied by more than 40%; the variation matches the Josephson-frequency variation with voltage. The linewidth of radiation is much smaller than expected from a purely cavity-induced synchronization. Thus, an additional mechanism seems to play a role. Some scenarios, related to the presence of the hot spot, are discussed.

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].…”

Terahertz wave emission from layered superconductors: Interferometer measurements

“…Fabrication of clear rectangular mesas with sharp edges [9] and emission characteristics of THz emitting mesas were reported. Hot spot is another important theme and is under intense investigation [10].…”

Synchronization in a one-dimensional array of point Josephson junctions coupled to a common load

“…The successful observations of coherent emission from cuprate superconductors renew the interests in understanding the synchronization of arrays of Josephson junctions [11][12][13][14][15][16][17] . Cuprate superconductors, such as Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO), are a natural realization of a stack of Josephson junctions of atomic thickness 18,19 , known as intrinsic Josephson junctions (IJJs).…”