High-transition-temperature superconductors such as the compound Bi₂Sr₂CaCu₂O₈ (BSCCO) have a layered structure. Here the copper oxide planes, which are responsible for superconductivity in these compounds, are separated by non-superconducting barrier layers (SrO and Bi₂O₃ in the case of BSCCO). Hence, these systems form intrinsic stacks of Josephson juntions, where the thickness of a single juntion is only approx. 1.5 nm (the layer sequence CuO₂-SrO/ Bi₂O₃-CuO₂ forms here an intrinsic junction). A 1 µm thick BSCCO single crystal consists of a stack of 666 of these junctions. Intrinsic Josephson junctions can oscillate at frequencies up to above 10 Terahertz. They are therefore of great importance, e.g. for the generation of electromagnetic radiation in particular in the terahertz regime.

The intrinsic Josephson effect was discovered in 1992 by R. Kleiner and P. Müller, and is intensively investigated worldwide.

Fig.1 (down below) : Schematic representation of intrinsic Josephson junctions in Bi₂Sr₂CaCu₂O₈, togehter with the crystal structure of the material (left). The blue layers represent the superconducting layers (CuO₂ layers), the transparent layers inbetween are the insulating barriers. The graph at the right shows part of a typical current-voltage-characteristic (IVC). The Josephson junctions in the stack can be switched individually between the zero-voltage and the resistive state. Hence, the IVC consists of many branches, which differ by the number of resistive junctions. In the figure, three of these branches are shown. The arrows indicate the direction of current ramp which was used to record the IVC.

R. Kleiner, H.-B. Wang. Bi₂Sr₂CaCu₂O₈ intrinsic Josephson junction stacks as emitters of terahertz radiation. Chapter 12, pp.383-408 in Superconductors at the Nanoscale, R. Wördenweber, V. Moshchalkov, S. Bending, F. Tafuri (eds.), de Gruyter (2017)

U. Welp, K. Kadowaki R. Kleiner. Superconducting emitters of THz radiation. Nature Photonics 7, 702-710 (2013)

R. Kleiner. Filling the Terahertz Gap. Science 318, 1254 (2007)

Y. Huang, H. Sun, D. An, X. Zhou, M. Ji, F. Rudau, R. Wieland, J. S. Hampp, O. Kizilaslan, J. Yuan, N. Kinev, O. Kiselev, V. P. Koshelets, J. Li, D. Koelle, R. Kleiner, B. Jin, J. Chen, L. Kang, W. Xu, H.-B. Wang, P. H. Wu. Self-mixing spectra of terahertz emitters based on Bi₂Sr₂CaCu₂O_8+δ intrinsic Josephson junction stacks. Phys. Rev. Applied 8, 054203 (2017)

H. Sun, Z. Yang, N. Kinev, O. Kiselev, Y. Lv, Y. Huang, L. Hao, M. Ji, X. Zhou, X. Tu, J. Li, F. Rudau, R. Wieland, J. S. Hampp, O. Kizilaslan, D. Koelle, R. Kleiner, V. P. Koshelets, H.-B. Wang, P. H. Wu. Terahertz spectroscopy of diluted gases using Bi₂Sr₂CaCu₂O_8+δ intrinsic Josephson junction stacks. Phys. Rev. Applied 8, 054005 (2017)

O. Kizilaslan, F. Rudau, R. Wieland, J. S. Hampp, X. J. Zhou, M. Ji, O. Kiselev, N. Kinev, Y. Huang, L. Y. Hao, A. Ishii, M. A. Aksan, T. Hatano, V. P. Koshelets, P. H. Wu, H. B. Wang, D. Koelle, R. Kleiner. Tuning THz emission properties of Bi₂Sr₂CaCu₂O_8+δ intrinsic Josephson junction stacks by charge carrier injection. Supercond. Sci. Technol. 30, 034006 (2017)

X. J. Zhou, M. Ji, D. Y. An, F. Rudau, R. Wieland, Q. Zhu, H. C. Sun, L. Y. Hao, D. Koelle, R. Kleiner, H. B. Wang, P. H. Wu, Modulating the emission properties of superconducting terahertz emitters, Terahertz Science and Technology 9, 60-70 (2016)

F. Rudau, R. Wieland, J. Langer, N. Kinev, J. Yuan, Y. Huang, M. Ji, X.J. Zhou, A. Ishii, P. H. Wu, T. Hatano, H. B. Wang, V. P. Koshelets, D. Koelle, R. Kleiner. 3D simulations of the electrothermal and THz emission properties of Bi₂Sr₂CaCu₂O₈ intrinsic Josephson junction stacks. Phys. Rev. Appl. 5, 044017 (2016)

X. J. Zhou, Q. Zhu, M. Ji, D. An, L. Hao, H. Sun, S. Ishida, F. Rudau, R. Wieland, J. Li, D. Koelle, H. Eisaki, Y. Yoshida, T. Hatano, R. Kleiner, H. B. Wang, P. H. Wu. Three-terminal stand-alone superconducting terahertz emitter: controlling the emission properties with movable hot spots. Appl. Phys. Lett. 107, 122602 (2015)

T. M. Benseman, A. E. Koshelev, V. Vlasko-Vlasov, Y. Hao, W.-K. Kwok, U. Welp, C. Keiser, B. Gross, M. Lange, D. Kölle, R. Kleiner, H. Minami, C. Watanabe, and K. Kadowaki. Current Filamentation in Large Bi₂Sr₂CaCu₂O_8+δ Mesa Devices Observed via Luminescent and Scanning Laser Thermal Microscopy. Phys. Rev. Appl. 3, 044017 (2015)

X. J. Zhou, J. Yuan, H. Wu, Z. S. Gao, M. Ji, D. Y. An, Y. Huang, F. Rudau, R. Wieland, N. Kinev, J. Li, A. Iishi, T. Hatano, V. P. Koshelets, D. Koelle, R. Kleiner, H. B. Wang, P. H. Wu. Tuning the terahertz emission power from an intrinsic Josephson junction stack with a focused laser beam. Phys. Rev. Appl. 3, 044012 (2015)

B. Gross, F. Rudau, N. Kinev, M. Tsujimoto, J. Yuan, Y. Huang, M. Ji, X. J. Zhou, D. Y. An, A. Iishi, P. H. Wu, T. Hatano, D. Koelle, H. B. Wang, V. P. Koshelets, R. Kleiner. Electrothermal behavior and terahertz emission properties of a planar array of two Bi₂Sr₂CaCu₂O_8+d intrinsic Josephson junction stacks. Supercond. Sci. Technol. 28, 055004 (2015)

F. Rudau, M. Tsujimoto, B. Gross, T. E. Judd, R. Wieland, E. Goldobin, N. Kinev, J. Yuan, Y. Huang, M. Ji, X. J. Zhou, D. Y. An, A. Iishi, R. G. Mints, P. H. Wu, T. Hatano, H. B. Wang, V. P. Koshelets, D. Koelle, R. Kleiner. Thermal and electromagnetic properties of Bi₂Sr₂CaCu₂O₈ intrinsic Josephson junction stacks studied via one-dimensional coupled sine-Gordon equations. Phys. Rev. B 91, 104513 (2015)

L. Y. Hao, M. Ji, J. Yuan, D. Y. An, M. Y. Li, X. J. Zhou, Y. Huang, H. C. Sun, Q. Zhu, F. Rudau, R. Wieland, N. Kinev, J. Li, W. W. Xu, B. B. Jin, J. Chen, T. Hatano, V. P. Koshelets, D. Koelle, R. Kleiner, H. B. Wang, P. H. Wu. A Compact Superconducting Terahertz Source Operating in Liquid Nitrogen. Phys. Rev. Appl. 3, 024006 (2015)

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. Modeling the linewidth dependence of coherent THz emission from intrinsic Josephson junction stacks in the hot-spot regime. Phys. Rev. B 88, 014524 (2013)

D. Y. An, J. Yuan, N. Kinev, M. Y. Li, Y. Huang, M. Ji, H. Zhang, Z. L. Sun, L. Kang, B. B. Jin, J. Chen, J. Li, B. Gross, A. Ishii, K. Hirata, T. Hatano, V. P. Koshelets, D. Koelle, R. Kleiner, H. B. Wang, W. W. Xu, P. H. Wu. Terahertz emission and detection both based on high-T_c superconductors: Towards an integrated receiver. Appl. Phys. Lett. 102, 092601 (2013)

B. Gross, S. Guénon, J. Yuan, M. Y. Li, J. Li, A. Iishi, R. G. Mints, T. Hatano, P. H. Wu, D. Koelle, H. B. Wang, R. Kleiner. Hot-spot formation in stacks of intrinsic Josephson junctions in Bi₂Sr₂CaCu₂O₈. Phys. Rev. B 86, 094524 (2012)

M. Y. Li, J. Yuan, N. Kinev, J. Li, B. Gross, S. Guénon, A. Ishii, K. Hirata, T. Hatano, D. Koelle, R. Kleiner, V. P. Koshelets, H. B. Wang, P. H. Wu. Linewidth dependence of coherent terahertz emission from Bi₂Sr₂CaCu₂O₈ intrinsic Josephson junction stacks in the hot-spot regime. Phys. Rev. B 86, 060505(R) (2012)

J. Yuan, M. Y. Li, B. Gross, A. Iishi, K. Yamaura, T. Hatano, K. Hirata, E. Takayama-Muromachi, P. H. Wu, D. Koelle, R. Kleiner, H. B. Wang. Terahertz emission from Bi₂Sr₂CaCu₂O_8+d intrinsic Josephson junction stacks with all-superconducting electrodes. Supercond. Sci. Technol. 25, 075015 (2012)

S. Guénon, M. Grünzweig, B. Gross, J. Yuan, Z. G. Jiang, Y. Y. Zhong, A. Iishi, P. H. Wu, T. Hatano, D. Koelle, H. B. Wang, R. Kleiner. Interaction of hot spots and terahertz waves in Bi₂Sr₂CaCu₂O₈ intrinsic Josephson junction stacks of various geometry. Phys. Rev. B 82, 214506 (2010)

H. B. Wang, S. Guénon, B. Gross, J. Yuan, Z. G. Jiang, Y. Y. Zhong, M. Grünzweig, A. Iishi, P. H. Wu, T. Hatano, D. Koelle, R. Kleiner. Coherent terahertz emission of intrinsic Josephson junction stacks in the hot spot regime. Phys. Rev. Lett. 105, 057002 (2010)

H. B. Wang, B. Y. Zhu, C. Gürlich, M. Ruoff, S. Kim, T. Hatano, B. R. Zhao, Z. X. Zhao, E. Goldobin, D. Koelle, and R. Kleiner. Fast Josephson Vortex Ratchet Made of Intrinsic Josephson Junctions in Bi₂Sr₂CaCu₂O8. Phys. Rev. B 80, 224507 (2009)

H. B. Wang, S. Guénon, J. Yuan, A. Iishi, S. Arisawa, T. Hatano, T. Yamashita, D. Koelle, and R. Kleiner. Hot Spots and Waves in Bi₂Sr₂CaCu₂O₈ Intrinsic Josephson Junction Stacks - a Study by Low Temperature Scanning Laser Microscopy. Phys. Rev. Lett. 102, 017006 (2009)

R. Kleiner. Filling the Terahertz Gap. Science 318, 5854, 1254 (2007)

T. Nachtrab, Ch. Bernhard, C. T. Lin, D. Koelle, and R. Kleiner. The Ruthenocuprates - Natural Superconductor-Ferromagnet Multilayers. Special Issue on 'Superconductivity and Magnetism', Comptes Rendus Physique Physique 7, 68 (2006)

T. Clauss, T. Ushida, M. Mößle, D. Koelle, and R. Kleiner. Imaging of µm Wavelength Collective Cavity Resonances in Bi₂Sr₂CaCu₂O_8+x Intrinsic Josephson Junction Stacks under Microwave Irradiation. Appl. Phys. Lett. 85, 3166 (2004)

T. Nachtrab, D. Koelle, R. Kleiner, Ch. Bernhard, and C. T. Lin. Intrinsic Josephson Effects in the Magnetic Superconductor RuSr₂GdCu₂O₈. Phys. Rev. Lett. 92, 117001 (2004)

Ch. Helm, L.N. Bulaevskii, D.A. Ryndyk, J. Keller, S. Rother, Y. Koval, P. Müller, R. Kleiner. Electronic compressibility and charge imbalance relaxation in cuprate superconductors. Physica C 408, 612 (2004)

S. Rother, Y. Koval, P. Müller, R. Kleiner, D.A. Ryndyk, J. Keller, C. Helm. Charge-imbalance effects in intrinsic Josephson systems. Phys. Rev. B 67, 024510 (2003)

T. Clauss, V. Oehmichen, M. Mößle, A. Müller, A. Weber, D. Koelle, R. Kleiner. Fluxons in long and annular intrinsic Josephson junction stacks. Supercond. Sci. Technol. 15, 1651 (2002)

S. Heim, M. Mößle, T. Clauß, and R. Kleiner. Fluxon modes in intrinsic Josephson junctions in Bi₂Sr₂CaCu₂O₈ single crystals. Supercond. Sci. Technol. 15, 1226 (2002)

C. Preis, C. Helm, J. Keller, A. Sergeev, R. Kleiner. Coupling of intrinsic Josephson oscillations in layered superconductors. In High-T_c Superconductors and Related Materials, S.-L. Drechsler, T. Mishonov (eds.), Kluwer Academic Publishers pp. 243-248 (2001)

S. Heim, T. Nachtrab, M. Mößle, R. Kleiner, R. Koch, S. Rother, O. Waldmann, P. Müller, T. Kimura, Y. Tokura. Intrinsic Tunneling in Cuprates and Manganites. Physica C 367, 348 (2002)

R. Kleiner, T. Gaber, G. Hechtfischer. Stacked Long Josephson Junctions in External Magnetic Fields - A Numerical Study of Coupled One-dimensional Sine-Gordon Equations. Physica C 362, 29 (2001)

A. Irie, G. Oya, R. Kleiner, P. Müller. Transport properties of Small-Sized Intrinsic Josephson Junctions in Bi₂Sr₂CaCu₂O_y. Physica C 362, 145 (2001)

C. Preis, C. Helm, K. Schmalzl, J. Keller, R. Kleiner, P. Müller. Phonons in intrinsic Josephson systems. Physica C 362, 51 (2001)

O. S. Chana, A. R. Kuzhakhmetov, P. A. Warburton, D. M. C. Hyland, C. R. M. Grovenor, D. Dew-Hughes, Y. Koval, R. Kleiner, P. Müller. Intrinsic Josephson junction in Tl-Ba-Ca-Cu-O thin films. Physica C 362, 265 (2001)

S. Rother, Y. Koval, P. Müller, R. Kleiner, Y. Kasai, K. Nakajima, M. Darula. FIR response of intrinsic Josephson junctions. IEEE Trans. Appl. Supercond. 11, 1191 (2001)

S. Rother, R. Kleiner, P. Müller, M. Darula, Y. Kasai, K. Nakajima. Far Infrared Response of Intrinsic Josephson Junctions. Physica C 341, 1565 (2000)

M. Mößle, R. Kleiner, R. Gatt, M. Onellion, P. Müller. Transport Measurements on Individual CuO₂ Double Layers. Physica C 341, 1571 (2000)

S. Heim, A. Irie, S. Schromm, M. Mößle, S. Rother, R. Kleiner, and P. Müller. Small Size Mesa Structures in Bi₂Sr₂CaCu₂O_8+d Single Crystals. Physica C 341, 1567 (2000)

R. Kleiner, T. Gaber, G. Hechtfischer. Stacked Long Josephson Junctions in Zero Magnetic Field - A Numerical Study of Coupled One-dimensional Sine-Gordon Equations. Phys. Rev. B 62, 4086 (2000)

A. Irie, S. Heim, S. Schromm, M. Mößle, T. Nachtrab, M. Gódo, R. Kleiner, P. Müller, G. Oya. Critical Currents of Small Bi₂Sr₂CaCu₂O_8+x Intrinsic Josephson Junction Stacks in External Magnetic Fields. Phys. Rev. B 62, 6681 (2000)

O. S. Chana, A. R. Kuzhakhmetov, P. A. Warburton, D. M. C. Hyland, D. Dew-Hughes, C. R. M. Grovenor, R. J. Kinsey, G. Burnell, W. E. Booij, M. G. Blamire, R. Kleiner, P. Müller. Alternating current Josephson effect in intrinsic Josephson bridges in Tl₂Ba₂CaCu₂O₈ thin films. Appl. Phys. Lett. 76, 3603 (2000)

A. V. Ustinov, E. Goldobin, G. Hechtfischer, N. Thyssen, A. Wallraff, R. Kleiner, P. Müller. Cherenkov Radiation from Josephson fluxons. Festkörperprobleme (1999)

M. Mößle, R. Kleiner. C-Axis Josephson Tunneling between Bi₂Sr₂CaCu₂O_8+x and Pb. Phys. Rev. B 59, 4486 (1999)

K. Schlenga, R. Kleiner, G. Hechtfischer, M. Mößle, S. Schmitt, P. Müller, Ch. Helm, Ch. Preis, F. Forsthofer, J. Keller, H. L. Johnson, M. Veith, and E. Steinbeiß. Tunneling spectroscopy with intrinsic Josephson junctions in Bi₂Sr₂CaCu₂O_8+d and Tl₂Ba₂Ca₂Cu₃O_10+d. Phys. Rev. B 57, 14518 (1998)

G. Hechtfischer, R. Kleiner, A. V. Ustinov, P. Müller. Josephson Vortex Motion in Stacks of Intrinsic Josephson Junctions in Bi₂Sr₂CaCu₂O_8+x. Appl. Supercond. 5, 303 (1998)

G. Yu. Logvenov, O. Waldmann, R. Kleiner, and P. Müller. Josephson vortex contribution to c-axis thermopower in Bi₂Sr₂CaCu₂O_8+d single crystals. Phys. Rev. B 58, 462 (1998)

W. Hanke, O. Schmitt, H. Endres, R. Kleiner, P. Müller. A microscopic model for the intrinsic Josephson tunneling in high T_c superconductors. Eur. Phys. J. B 5, 465 (1998)

G. Hechtfischer, R. Kleiner, K. Schlenga, W. Walkenhorst, P. Müller and H. L. Johnson. Collective motion of Josephson vortices in intrinsic Josephson junctions in Bi₂Sr₂CaCu₂O_8+y. Phys. Rev. B 55, 14638 (1997)

G. Hechtfischer, W. Walkenhorst, G. Kunkel, K. Schlenga, R. Kleiner, P. Müller, and H. L. Johnson. High Frequency Applications of Intrinsic Josephson Junctions in Mesa Structures on Bi₂Sr₂CaCu₂O_8+y Single Crystals. IEEE Trans. Appl. Supercond. 7, 2723 (1997)

R. Kleiner, M. Mößle, W. Walkenhorst, G. Hechtfischer, K. Schlenga, and P. Müller. Supercurrents in c-axis Pb/Bi₂Sr₂CaCu₂O₈ tunnel junctions. Physica C 282, 2435 (1997)

K. Schlenga, G. Hechtfischer, W. Walkenhorst, H. L. Johnson, F. Forsthofer, Ch. Helm, Ch. Preis, J. Keller, R. Kleiner, and Paul Müller. C-axis tunneling between adjacent superconducting CuO₂ bi- or trilayers. Physica C 282, 2431 (1997)

R. Kleiner, P. Müller. Intrinsic Josephson Effects in Layered Superconductors. Physica C 293, 156 (1997)

Ch. Helm, Ch. Preis, F. Forsthofer, J. Keller, K. Schlenga, R. Kleiner, and P. Müller. Subgap structures in the current-voltage characteristic of the intrinsic Josephson effect due to phonons. Physica C 293, 60 (1997)

H. L. Johnson, G. Hechtfischer, G. Götz, R. Kleiner, and P. Müller. Zero Crossing Steps in Intrinsic Josephson Junctions of Bi₂Sr₂CaCu₂O_8+d. J. Appl. Phys. 82, 756 (1997)

Ch. Helm, Ch. Preis, F. Forsthofer, J. Keller, K. Schlenga, R. Kleiner, and P. Müller. Coupling between phonons and intrinsic Josephson oscillations in cuprate superconductors. Phys. Rev. Lett. 79, 737 (1997)

G. Hechtfischer, R. Kleiner, A. V. Ustinov, and P. Müller. Non-Josephson emission from intrinsic junctions in Bi₂Sr₂CaCu₂O_8+y: Cherenkov radiation by Josephson vortices. Phys. Rev. Lett. 79, 1365 (1997)

W. Walkenhorst, G. Hechtfischer, S. Schlötzer, R. Kleiner, P. Müller. Probing the collective Josephson Plasma Resonance in Bi₂Sr₂CaCu₂O_8+y by W-Band Mixing Experiments. Phys. Rev. B 56, 8396 (1997)

K. Schlenga, G. Hechtfischer, R. Kleiner, W. Walkenhorst, P. Müller, H.L. Johnson. Subgap Structures in Intrinsic Josephson Junctions of Tl₂Ba₂Ca₂Cu₃O₁₀ and Bi₂Sr₂CaCu₂O_8+d. Czechoslovak Journal of Physics 46, 1277 (1996)

K. Schlenga, G. Hechtfischer, R. Kleiner, W. Walkenhorst, P. Müller, H.L. Johnson, M. Veith, W. Brodkorb, E. Steinbeiß. Subgap Structures in Intrinsic Josephson Junctions of Tl₂Ba₂Ca₂Cu₃O₁₀ and Bi₂Sr₂CaCu₂O_8+d. Phys. Rev. Lett. 76, 4943 (1996)

R. Kleiner. Intrinsic Josephson Junctions in High Temperature Superconductors. J. Low Temp. Phys. 106, 453 (1996)

K. Schlenga, W. Biberacher, G. Hechtfischer, R. Kleiner, B. Schey, O. Waldmann, W. Walkenhorst, P. Müller, F.X. Régi, H. Savary, J. Schneck, M. Brinkmann, H. Bach, K. Westerholt, G. Winkel. Intrinsic Josephson Effects in Various Layered Superconductors. Physica C 235, 3273 (1995)

R. Kleiner, P. Müller. Intrinsic Josephson effects in high-T_c- superconductors. Phys. Rev. B 49, 1327 (1994)

R. Kleiner, P.Müller, H. Kohlstedt, N.F. Pedersen, S. Sakai. Dynamic behaviour of Josephson-coupled layered structures. Phys. Rev. B 50, 3942 (1994)

R. Kleiner. Two-dimensional resonant modes in stacked Josephson junctions. Phys. Rev B 50, 6919 (1994)

R. Kleiner, B. Aigner, B. Avenhaus, C. Kreuzer, P. Pospischil, F. Steinmeyer, P. Müller, K. Andres. Intrinsic Josephson Effects in High-T_c Single Crystals. Physica B 194, 1753 (1994)

F.-X. Régi, J. Schneck, H. Savary, R. Mellet, P. Müller and R. Kleiner. Resistivity anisotropy and Josephson coupling in lead-substituted bismuth cuprates. J. Phys. III France 4, 2249 (1994)

B. Aigner, B. Avenhaus, R. Kleiner, C. Kreuzer, G. Kunkel, P. Pospischil, F. Steinmeyer, P. Müller, K. Andres. Intrinsic Josephson Effects in Bi₂CaSr₂Cu₂O₈ Single Crystals. IEEE Transactions on Applied Superconductivity 3, 2281 (1993)

R. Kleiner, F. Steinmeyer, G. Kunkel, P. Müller. Intrinsic Josephson Effects in Bi₂CaSr₂Cu₂O₈ Single Crystals. Phys. Rev. Lett. 68, 2394 (1992); siehe auch: Colin Pegrum, Natural Josephson Junctions, Nature 358, 193 (1992); A single-crystal route to tunneling, Science News 142, 92 (1992)

R. Kleiner, F. Steinmeyer, G. Kunkel, P. Müller. Observation of Josephson Coupling between CuO double Layers in Bi₂CaSr₂Cu₂O₈ Single Crystals. Physica C 185, 2617 (1991)