IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 24, NO. 4, AUGUST 2014 1800205 The Resonant Interaction of Intrinsic Josephson Junctions With Standing Waves A. Grib, M. Mans, M. Büenfeld, J. Scherbel, F. Schmidl, H. Schneidewind, and P. Seidel (Invited Paper) Abstract—IV-characteristics of shunted microbridges made of Tl 2 Ba 2 CaCu 2 O 8 (TBCCO) were measured. The TBCCO films were grown epitaxially on 20 ◦ misaligned LaAlO 3 substrates and then covered by the gold shunting layer. Each of the microbridges consisted of about 360 shunted intrinsic Josephson junctions. Self- induced resonant particularities with a main period of about 17 mV were found on IV-curves. We showed that these partic- ularities did not depend on the characteristics of the individual junctions and that they were connected with the geometrical dimensions of the system. The origin of particularities was the interaction of Josephson generation with the standing wave ap- peared in the system. We modeled this interaction considering radiation of junctions into the transmission line and found that the model described the main resonant structure of IV-characteristics. Strong synchronization of junctions appeared in the vicinity of the first particularity. Index Terms—Coherent radiation, high-temperature supercon- ductors, intrinsic Josephson junctions, synchronization. I. I NTRODUCTION D UE TO high density and the high frequency of radia- tion (up to 3–4 THz), intrinsic Josephson junctions in high-temperature superconductors are promising candidates to be used as sources of high-frequency radiation [1]. It was shown recently that intrinsic Josephson junctions can radiate coherently in the mesa structures [1]–[3]. The synchronizing mechanism in this case is the interaction of the Josephson generation of junctions with the standing wave which is created inside the structure by this generation. However, due to the highly inhomogeneous distribution of currents and voltages inside the mesa structure, the wide distribution of temperatures up to the appearance of the so-called hot spots [3] impedes the creation of the powerful sources of radiation. The use Manuscript received December 19, 2013; revised January 28, 2014; accepted February 3, 2014. Date of publication March 12, 2014; date of current version April 3, 2014. This paper was recommended by Associate Editor A. Kleinsasser. A. Grib is with the Institut für Festkörperphysik, Friedrich-Schiller- Universität Jena, D-07743 Jena, Germany and with the Physics Department, Kharkiv V. N. Karazin National University, 61022 Kharkiv, Ukraine (e-mail: alexander.gryb@googlemail.com). M. Mans, M. Büenfeld, J. Scherbel, F. Schmidl, and P. Seidel are with the Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena, D-07743 Jena, Germany (e-mail: paul.seidel@uni-jena.de). H. Schneidewind is with the Institut für Photonische Technologien e.V., D-07745 Jena, Germany. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TASC.2014.2311447 of the linear arrays of intrinsic junctions can be the solution of this problem because the cooling of thin microbridges is more effective than the cooling of thick mesas. In the present paper we show that the same mechanism of the interaction of Josephson generation with the standing wave is valid for planar arrays of intrinsic junctions as it is valid for mesas contained intrinsic junctions. We show that in the IV-characteristics of microbridges containing intrinsic junctions there appear self- induced resonant particularities which origin is the interaction between the Josephson generation and the standing wave. We model this interaction by means of the coupling of the array with the transmission line and show that synchronization of the radiation of junctions appears in the vicinity of mentioned resonant particularities. II. THE PREPARATION OF THE SAMPLES Tl 2 Ba 2 CaCu 2 O 8 films with thickness of 150 nm were grown on 20 ◦ misaligned LaAlO 3 substrates. Details of the preparation are described elsewhere [4]. The gold layer of about 10 nm was sputtered on the top of the TBCCO film. Then patterning of the structure was made and microbridges with dimensions 2 × 2 μm 2 were obtained. Each of the microbridges contained about 360 intrinsic junctions. Microbridges were integrated into the bow-tie resonator structures with the resonant frequency of about 500 GHz. The obtained structures were connected to con- tact pads by current lines containing the antenna-like elements (Fig. 1). The IV-characteristics of samples were measured by means of the two-probe method. III. RESULTS OF THE EXPERIMENTS In this paper we discuss IV-characteristics of two samples. We will call them as the sample A and the sample B, both with the same total length. The IV-characteristics of the sample A are shown in Fig. 2. Shunting leads to changes of the IV-curve of the system. The IV- characteristic of shunted junctions does not have the hysteresis below the critical current as well as the multibranch behavior which usually appears in IV-curves of high-temperature superconductors. However, separate mea- surements of the same sample give different IV-characteristics. In Fig. 2 we showed three measurements of the IV-curve of the same sample made at different times after the preparation. The resistance of the system calculated at large bias currents was about 4 Ohm at the first measurement (Fig. 2, curve 1), whereas at the second measurement it became 14.5 Ohm and 1051-8223 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. 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