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  • 1.
    Borodianskyi, Evgenii A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Krasnov, Vladimir M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Josephson emission with frequency span 1–11 THz from small Bi2Sr2CaCu2O8+δ mesa structures2017Ingår i: Nature Communications, E-ISSN 2041-1723, Vol. 8, artikel-id 1742Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mesa structures made of Bi2Sr2CaCu2O8+δ high-temperature superconductor represent stacks of atomic scale intrinsic Josephson junctions. They can be used for generation of high-frequency electromagnetic waves. Here we analyze Josephson emission from small-but-high mesas (with a small area, but containing many stacked junctions). We have found strong evidence for tunable terahertz emission with a good efficacy in a record high-frequency span 1–11 THz, approaching the theoretical upper limit for this superconductor. Emission maxima correspond to in-phase cavity modes in the mesas, indicating coherent superradiant nature of the emission. We conclude that terahertz emission requires a threshold number of junctions N ~ 100. The threshold behavior is not present in the classical description of stacked Josephson junctions and suggests importance of laser-like cascade amplification of the photon number in the cavity. 

  • 2.
    Borodianskyi, Ievgenii
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Superradiant THz wave emission from arrays of Josephson junctions2020Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    High-power, continuous-wave, compact and tunable THz sources are needed for a large variety of applications. Development of power-efficient sources of electromagnetic radiation in the 0.1-10 THz range is a difficult technological problem, known as the “THz gap.” Josephson junctions allow creation of monochromatic THz sources with an inherently broad range of tunability. However, emission power from a single junction is too small. It can be amplified in a coherent superradiant manner by phase-locking of many junctions. In this case, the emission power should increase as a square of the number of phase-locked junctions.The aim of this thesis is to study a possibility of achieving coherent super-radiant emission with significant power and frequency tunability from Joseph-son junction arrays. Two types of devices are studied, based either on stacks (one-dimensional arrays) of intrinsic Josephson junctions naturally formed in single crystals of high-temperature cuprate superconductor Bi2Sr2CaCu2O8+x, or two-dimensional arrays of artificial low-temperature superconducting Nb/NbSi/Nb junctions. Micron-size junctions are fabricated using micro- and nanofabrication tools.The first chapter of this thesis describes the theory of Josephson junctions and how mutual coupling between Josephson junctions can lead to self-syn-chronization, facilitating the superradiant emission of electromagnetic radia-tion. The second chapter is focused on the technical aspects of this work, with detailed descriptions of sample fabrication and experimental techniques. The third chapter presents main results and discussion. It is demonstrated that de-vices based on high-Tc cuprates allow tunable emission in a very broad fre-quency range 1-11 THz. For low- Tc junction arrays synchronization of up to 9000 junctions is successfully achieved. It is argued that an unconventional traveling-waves mechanism facilitates the phase-locking of such huge arrays. The obtained results confirm a possibility of creation of high-power, continu-ous-wave, compact and tunable THz sources, based on arrays of Josephson junctions.

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  • 3.
    Cattaneo, Roger
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Borodianskyi, Evgenii A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kalenyuk, Aleksey A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. National Academy of Sciences of Ukraine, Ukraine.
    Krasnov, Vladimir M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Moscow Institute of Physics and Technology, Russia.
    Superconducting Terahertz Sources with 12% Power Efficiency2021Ingår i: Physical Review Applied, E-ISSN 2331-7019, Vol. 16, nr 6, artikel-id L061001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Low power efficiency is one of the main problems of terahertz (THz) sources, colloquially known as “the THz gap.” In this work we present prototypes of THz devices based on whisker crystals of a high-temperature superconductor Bi2Sr2CaCu2O8+δ with a record high-radiation power efficiency of 12% at a frequency of approximately 4 THz. We employ various on- and off-chip detection techniques and, in particular, use the radiative cooling phenomenon for accurate evaluation of the emission power. We conclude that such devices can be used for creation of tunable, monochromatic, cw, compact, and power-efficient THz sources.

  • 4.
    de Andrés Prada, Roberto
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. University of Fribourg, Switzerland.
    Golod, Taras
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kapran, Olena M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Borodianskyi, Evgenii A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Bernhard, Ch.
    Krasnov, Vladimir M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Moscow Institute of Physics and Technology, Russia.
    Memory-functionality superconductor/ferromagnet/superconductor junctions based on the high-Tc cuprate superconductors YBa2Cu3O7−x and the colossal magnetoresistive manganite ferromagnets La2/3X1/3MnO3+δ(X=Ca,Sr)2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 21, artikel-id 214510Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Complex oxides exhibit a variety of unusual physical properties, which can be used for designing novel electronic devices. Here we fabricate and study experimentally nanoscale superconductor/ferromagnet/ superconductor junctions with the high-Tc cuprate superconductors YBa2Cu3O7−x and the colossal magnetoresistive (CMR) manganite ferromagnets La2/3X1/3MnO3+δ(X=CaorSr). We demonstrate that in a broad temperature range the magnetization of a manganite nanoparticle, forming the junction interface, switches abruptly in a monodomain manner. The CMR phenomenon translates the magnetization loop into a hysteretic magnetoresistance loop. The latter facilitates a memory functionality of such a junction with just a single CMR ferromagnetic layer. The orientation of the magnetization (stored information) can be read out by simply measuring the junction resistance in a finite magnetic field. The CMR facilitates a large readout signal in a small applied field. We argue that such a simple single-layer CMR junction can operate as a memory cell both in the superconducting state at cryogenic temperatures and in the normal state up to room temperature.

  • 5. Galin, M. A.
    et al.
    Rudau, F.
    Borodianskyi, Evgenii A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kurin, V. V.
    Koelle, D.
    Kleiner, R.
    Krasnov, Vladimir M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Moscow Institute of Physics and Technology, Russia.
    Klushin, A. M.
    Direct Visualization of Phase-Locking of Large Josephson Junction Arrays by Surface Electromagnetic Waves2020Ingår i: Physical Review Applied, E-ISSN 2331-7019, Vol. 14, nr 2, artikel-id 024051Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Phase-locking of oscillators leads to super-radiant amplification of the emission power. This is particularly important for development of terahertz sources, which suffer from low emission efficiency. In this work we study large Josephson junction arrays containing several thousand Nb-based junctions. Using low-temperature scanning laser microscopy, we observe that at certain bias conditions two-dimensional standing-wave patterns are formed, manifesting themselves as global synchronization of the arrays. Analysis of standing waves indicates that they are formed by surface plasmon-type electromagnetic waves propagating at the electrode-substrate interface. Thus, we demonstrate that surface waves provide an effective mechanism for long-range coupling and phase-locking of large junction arrays.

  • 6.
    Galin, Mikhail A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Institute for Physics of Microstructures RAS, Russia.
    Borodianskyi, Evgenii A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kurin, V. V.
    Shereshevskiy, I. A.
    Vdovicheva, N. K.
    Krasnov, Vladimir M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Klushin, A. M.
    Synchronization of Large Josephson-Junction Arrays by Traveling Electromagnetic Waves2018Ingår i: Physical Review Applied, E-ISSN 2331-7019, Vol. 9, nr 5, artikel-id 054032Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mutual synchronization of many Josephson junctions is required for superradiant enhancement of the emission power. However, the larger the junction array is, the more difficult is the synchronization, especially when the array size becomes much larger than the emitted wavelength. Here, we study experimentally Josephson emission from such larger-than-the-wavelength Nb/NbSi/Nb junction arrays. For one of the arrays we observe a clear superradiant enhancement of emission above a threshold number of active junctions. The arrays exhibit strong geometrical resonances, seen as steps in current-voltage characteristics. However, radiation patterns of the arrays have forward-backward asymmetry, which is inconsistent with the solely geometrical resonance (standing-wave) mechanism of synchronization. We argue that the asymmetry provides evidence for an alternative mechanism of synchronization mediated by unidirectional traveling-wave propagation along the array (such as a surface plasmon). In this case, emission occurs predominantly in the direction of propagation of the traveling wave. Our conclusions are supported by numerical modeling of Josephson traveling-wave antenna. We argue that such a nonresonant mechanism of synchronization opens a possibility for phase locking of very large arrays of oscillators.

  • 7.
    Galin, Mikhail A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Institute for Physics of Microstructures RAS, Russia.
    Borodianskyi, Ievgenii A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kurin, V. V.
    Shereshevskiy, I. A.
    Vdovicheva, N. K.
    Krasnov, Vladimir M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Klushin, A. M.
    Evidence of synchronization of large Josephson-junction arrays by traveling electromagnetic waves2018Ingår i: EPJ Web of Conferences, E-ISSN 2100-014X, Vol. 195, artikel-id 02004Artikel i tidskrift (Refereegranskat)
  • 8.
    Kalenyuk, Aleksey A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Institute of Metal Physics of National Academy of Sciences of Ukraine, Ukraine; Kyiv Academic University, Ukraine.
    Borodianskyi, Evgenii A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kordyuk, A. A.
    Krasnov, Vladimir M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Moscow Institute of Physics and Technology, Russia.
    Influence of the Fermi surface geometry on the Josephson effect between iron-pnictide and conventional superconductors2021Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, nr 21, artikel-id 214507Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study hybrid Josephson junctions between a multiband Ba1-xNaxFe2As2 iron-pnictide and Nb. We observe that the insertion of a Cu interlayer in such junctions leads to a dramatic enhancement of the IcRn product, despite the weaker proximity-induced superconductivity of Cu. This counterintuitive phenomenon is attributed to the differences in Fermi surface geometries of Nb and Cu, which affect the selectivity of tunneling in sign-reversal s± bands of pnictide. Our results indicate that the sensitivity to Fermi surface geometries provides a new tool for phase-sensitive studies and paves the way to conscious Fermi surface engineering of pnictide junctions.

  • 9.
    Kalenyuk, Aleksey A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Institute of Metal Physics of National Academy of Sciences of Ukraine, Ukraine.
    Pagliero, Alessandro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Borodianskyi, Evgenii A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Aswartham, S.
    Wurmehl, S.
    Büchner, B.
    Chareev, D. A.
    Kordyuk, A. A.
    Krasnov, Vladimir M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Unusual two-dimensional behavior of iron-based superconductors with low anisotropy2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 13, artikel-id 134512Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study angular-dependent magnetoresistance in iron-based superconductors Ba1−xNaxFe2As2 and FeTe1−xSex. Both superconductors have relatively small anisotropies γ∼2 and exhibit a three-dimensional (3D) behavior at low temperatures. However, we observe that they start to exhibit a profound two-dimensional behavior at elevated temperatures and in applied magnetic field parallel to the surface. We conclude that the unexpected two-dimensional (2D) behavior of the studied low-anisotropic superconductors is not related to layeredness of the materials, but is caused by appearance of surface superconductivity when magnetic field exceeds the upper critical field Hc2(T) for destruction of bulk superconductivity. We argue that the corresponding 3D-2D bulk-to-surface dimensional transition can be used for accurate determination of the upper critical field.

  • 10.
    Kalenyuk, Aleksey A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Institute of Metal Physics of National Academy of Sciences of Ukraine, Ukraine.
    Pagliero, Alessandro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Borodianskyi, Evgenii A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kordyuk, A. A.
    Krasnov, Vladimir M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Phase-Sensitive Evidence for the Sign-Reversal s± Symmetry of the Order Parameter in an Iron-Pnictide Superconductor Using Nb/Ba1−xNaxFe2As2 Josephson Junctions2018Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, nr 6, artikel-id 067001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Josephson current provides a phase-sensitive tool for probing the pairing symmetry. Here we present an experimental study of high-quality Josephson junctions between a conventional s-wave superconductor Nb and a multiband iron-pnictide Ba1−xNaxFe2As2. Junctions exhibit a large enough critical current density to preclude the d-wave symmetry of the order parameter in the pnictide. However, the IcRn product is very small ≃3μV, which is not consistent with the sign-preserving s++ symmetry either. We argue that the small IcRn value, along with its unusual temperature dependence, provides evidence for the sign-reversal s± symmetry of the order parameter in Ba1−xNaxFe2As2. We conclude that it is the phase sensitivity of our junctions that leads to an almost complete (below a subpercent) cancellation of supercurrents from sign-reversal bands in the pnictide.

  • 11.
    Kapran, Olena M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Morari, Roman
    Golod, Taras
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Borodianskyi, Evgenii A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Boian, Vladimir
    Prepelita, Andrei
    Klenov, Nikolay
    Sidorenko, Anatoli S.
    Krasnov, Vladimir M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. State University, Russia.
    In situ transport characterization of magnetic states in Nb/Co superconductor/ferromagnet heterostructures2021Ingår i: Beilstein Journal of Nanotechnology, ISSN 2190-4286, Vol. 12, s. 913-923Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Employment of the non-trivial proximity effect in superconductor/ferromagnet (S/F) heterostructures for the creation of novel superconducting devices requires accurate control of magnetic states in complex thin-film multilayers. In this work, we study experimentally in-plane transport properties of microstructured Nb/Co multilayers. We apply various transport characterization techniques, including magnetoresistance, Hall effect, and the first-order-reversal-curves (FORC) analysis. We demonstrate how FORC can be used for detailed in situ characterization of magnetic states. It reveals that upon reduction of the external field, the magnetization in ferromagnetic layers first rotates in a coherent scissor-like manner, then switches abruptly into the antiparallel state and after that splits into the polydomain state, which gradually turns into the opposite parallel state. The polydomain state is manifested by a profound enhancement of resistance caused by a flux-flow phenomenon, triggered by domain stray fields. The scissor state represents the noncollinear magnetic state in which the unconventional odd-frequency spin-triplet order parameter should appear. The non-hysteretic nature of this state allows for reversible tuning of the magnetic orientation. Thus, we identify the range of parameters and the procedure for in situ control of devices based on S/F heterostructures.

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