Abstract-Bridging the terahertz gap for chaotic sources with superconducting junctions

D. R. Gulevich, V. P. Koshelets, and F. V. Kusmartsev

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.99.060501

We observe a broadband chaotic signal of terahertz frequency emitted from a superconducting junction. The generated radiation has a wide spectrum reaching 0.7 THz and power sufficient to drive on-chip circuit elements. Our experimental finding is fully confirmed by numerical modeling based on microscopic theory and reveals the unrealized potential of superconducting systems in chaos-based terahertz communication, fast generation of true random numbers, and noninvasive terahertz spectroscopy.

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Abstract-Three-Dimensional Simulations of the Electrothermal and Terahertz Emission Properties of Bi2Sr2CaCu2O8 Intrinsic Josephson Junction Stacks

F. Rudau, R. Wieland, J. Langer, X. J. Zhou, M. Ji, N. Kinev, L. Y. Hao, Y. Huang, J. Li, P. H. Wu, T. Hatano, V. P. Koshelets, H. B. Wang, D. Koelle, and R. Kleiner

Phys. Rev. Applied 5, 044017 – Published 27 April 2016

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.5.044017

We use 2D coupled sine-Gordon equations combined with 3D heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a 250×70  μm2intrinsic Josephson junction stack. The 700 junctions are grouped to 20 segments; we assume that in a segment all junctions behave identically. At large input power, a hot spot forms in the stack. Resonant electromagnetic modes oscillating either along the length [(0, n) modes] or the width [(m, 0) modes] of the stack or having a more complex structure can be excited both with and without a hot spot. At fixed bath temperature and bias current, several cavity modes can coexist in the absence of a magnetic field. The (1, 0) mode considered to be the most favorable mode for terahertz emission can be stabilized by applying a small magnetic field along the length of the stack. A strong field-induced enhancement of the emission power is also found in experiment for an applied field around 5.9 mT.

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Abstract-Tuning the Terahertz Emission Power of an Intrinsic Josephson-Junction Stack with a Focused Laser Beam

X. J. Zhou, J. Yuan, H. Wu, Z. S. Gao, M. Ji, D. Y. An, Y. Huang, F. Rudau, R. Wieland, B. Gross, N. Kinev, J. Li, A. Ishii, T. Hatano, V. P. Koshelets, D. Koelle, R. Kleiner, H. B. Wang, and P. H. Wu

Phys. Rev. Applied 3, 044012 – Published 21 April 2015

http://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.3.044012

We report on tuning the THz emission of a Bi2Sr2CaCu2O8 (BSCCO) intrinsic Josephson-junction stack by a focused laser beam which is scanned across the stack. The emission power Pe increases by up to 75% upon laser irradiation for a bath temperature near 22 K. The laser-induced changes in the voltage Vdc across the stack and in the emission power are measured simultaneously. The maximum of the laser-induced changes in emission power ΔPe is achieved by irradiating the stack on the location where the local temperature is about the critical temperature Tc. However, ΔPe is found to be proportional to the laser-induced global voltage change ΔVdc, irrespective of the laser position. This unexpected global response is likely to be related to a change in the average stack temperature and is consistent with the change in Pe when increasing the bath temperature by about 0.2 K. This tuning method can be employed in the application of BSCCO THz sources.

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Abstract-Modeling the linewidth dependence of coherent terahertz emission from intrinsic Josephson junction stacks in the hot-spot regime

B. Gross, J. Yuan, D.Y. An, M. Y. Li, N. Kinev, X. J. Zhou, M. Ji, Y. Huang, T. Hatano, R.G. Mints,V. P. Koshelets, P.H. Wu, H. B. Wang, D. Koelle, R. Kleiner

http://arxiv.org/abs/1307.3391

Recently it has been found that, when operated at large input power, the linewidth of terahertz radiation emitted from intrinsic Josephson junction stacks can be as narrow as some megahertz. In this high-bias regime a hot spot coexists with regions which are still superconducting. Surprisingly, the linewidth was found to decrease with increasing bath temperature. We present a simple model describing the dynamics of the stack in the presence of a hot spot by two parallel arrays of pointlike Josephson junctions and an additional shunt resistor in parallel. Heat diffusion is taken into account by thermally coupling all elements to a bath at temperature T_b. We present current-voltage characteristics of the coupled system and calculations of the linewidth of the radiation as a function of T_b. In the presence of a spatial gradient of the junction parameters critical current and resistance, the linewidth deceases with increasing T_b, similar to the experimental observation.