| 1. |
- Kornev, V. K., et al.
(författare)
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Dynamics of underdamped Josephson junctions with non-sinusoidal current-phase relation
- 2006
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 435:1-2, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- Results on analytical and computational investigations of high-frequency dynamics of Josephson junctions, characterized by non-zero capacitance and the second harmonic in the current-phase relation are presented. These attributes each have influence on the behaviour of integer Shapiro steps and lead to the formation of non-integer Shapiro steps. Analytic theory of the integer and non-integer Shapiro steps has been developed for the so-called high-frequency limit. The analytical and numerical results are compared with experimental data for hybrid heterostructures YBCO/Au/Nb. Detector response for the case of high fluctuation level has been considered as well.
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| 2. |
- Ovsyannikov, Gennady, 1948, et al.
(författare)
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Triplet superconductivity in oxide ferromagnetic interlayer of mesa-structure
- 2014
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 592:1, s. Art. no. 012136-
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Konferensbidrag (refereegranskat)abstract
- We present experimental data on Nb-Au/La0.7Sr0.3MnO3/SrRuO3/YBa2Cu3O7-δ mesa- structure with in plane linear size 10÷50 μm. The mesa-structures were patterned from the epitaxial heterostructures fabricated by pulsed laser ablation and magnetron sputtering. Superconducting critical current was observed for mesa-structures with the interlayer thicknesses up to 50 nm. In the mesa-structures with just one, either La0.7Sr0.3MnO3 or SrRuO3 interlayer with a thickness larger than 10 nm no superconducting current was observed. The registered superconducting current for the mesa-structures with a thinner interlayer is attributed to pinholes. Obtained results are discussed in terms of superconducting long-range triplet generation at interfaces of superconductor and a composite ferromagnet consisting of ferromagnetic materials with non-collinear magnetization.
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| 3. |
- Constantinian, K. Y., et al.
(författare)
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Interfaces in superconducting hybrid heterostructures with an antiferromagnetic interlayer
- 2013
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Ingår i: Physics of the Solid State. - 1063-7834 .- 1090-6460. ; 55:3, s. 461-465
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Tidskriftsartikel (refereegranskat)abstract
- The structural, X-ray diffraction, and electrophysical studies of hybrid superconducting hetero-structures with an interlayer of cuprate antiferromagnetic Ca1 - x Sr (x) CuO2 (CSCO) with the upper electrode Nb/Au and the lower electrode Y(B)a(2)Cu(3)O(7 - delta) (YBCO) have been carried out. It has been experimentally shown that the epitaxial growth of two cuprates, YBCO and CSCO, results in the formation of an interface on which the enrichment of the CSCO interlayer with charge carriers proceeds to a depth of about 20 nm. In this case, the conduction of the enriched CSCO region proves to be closer to metallic, whereas the CSCO film deposited onto the NdGaO3 substrate is a Mott insulator with hopping conduction.
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| 4. |
- Constantinian, K. Y., et al.
(författare)
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Spin-Triplet Superconducting Current in Metal-Oxide Heterostructures With Composite Ferromagnetic Interlayer
- 2016
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 26:3
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Tidskriftsartikel (refereegranskat)abstract
- Superconducting heterostructures fabricated from oxide superconductor YBa2Cu2O7-delta and a composite ferromagnet La0.7Sr0.3MnO3/SrRuO3 interlayer and Au/Nb counter electrode were studied experimentally. Superconducting current was observed at magnetic field H raised up to 2000 Oe, which is greater than saturation magnetic field of manganite La0.7Sr0.3MnO3 (of order 100 Oe) and greater by a few orders than the value of magnetic field corresponding to penetration of one magnetic flux quantum. Microwave measurements of integer and half-integer Shapiro steps in conditions when relatively low external magnetic fieldH < 30 Oe was applied showed that the second harmonic in the current-phase relation of superconducting current becomes as big as the first harmonic. Fourier analysis of I-C(H) dependence allows extracting the components of fractional periods in I-C(H) function that also confirms a deviation from the sinusoidal current-phase relation. The obtained experimental data are explained by theoretical models that predict a huge enhancement of the second harmonic of the spin-triplet component in the superconducting current. The current-phase relation could be controlled by an external magnetic field, changing the directions of magnetization in the composite bilayer ferromagnet, which is inserted between two spin-singlet superconductors.
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| 5. |
- Kislinskiǐ, Yu V., et al.
(författare)
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Copper oxide superconducting/antiferromagnetic interface
- 2015
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Ingår i: Solid State Phenomena. - 1662-9779 .- 1012-0394. - 9783038354826 ; 233-234, s. 733-736
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Konferensbidrag (refereegranskat)abstract
- Superconducting Nb/Au/Ca1-xSrxCuO2/YBa2Cu3O7 mesa-heterostructures were investigated. Dependencies of electrical parameters versus inverse capacitance were measured. A band diagram which takes into account an accumulation of holes inCa1-xSrxCuO2 interlayer and band bending due to difference of work functions was proposed. The dependencies of electrical parameters were analyzed by examining the quasipartical and superconducting currents.
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| 6. |
- Ovsyannikov, Gennady, 1948, et al.
(författare)
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Magnetic proximity effect and superconducting triplet correlations at the cuprate superconductor and oxide spin valve interface
- 2016
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 42:10, s. 873-883
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Tidskriftsartikel (refereegranskat)abstract
- A heterostructure consisting of a cuprate superconductor YBa2Cu3O7-delta and a ruthenate/manganite (SrRuO3/La0.7Sr0.3MnO3) spin valve was studied using SQUID magnetometry, ferromagnetic resonance, and neutron reflectometry. It is shown that because of the magnetic proximity effect a magnetic moment is excited in the superconducting portion of the heterostructure, whereas the magnetic moment in the spin valve becomes suppressed. The experimentally obtained value of a typical penetration depth of a magnetic moment into the superconductor is significantly greater than the coherence length of the cuprate superconductor, which indicates that the induced magnetic moment mechanism of Cu atoms is dominant. The mesastructure prepared by adding niobium film as a second superconducting electrode to the existing heterostructure, exhibited a superconducting current (dc Josephson effect) at interlayer thicknesses that are much greater than the coherence length of the ferromagnetic materials. The maximum of the critical current density dependence on the thickness of the spin valve material corresponds to the interlayer coherence length, which agrees with the theoretical predictions associated with spin-triplet pairing. The superconducting current is observed at magnetic fields that are two orders of magnitude greater than the field corresponding to the occurrence of one magnetic flux quantum in the mesastructure. The ratio of the second harmonic of the current-phase dependence of the mesastructure superconducting current to the first, determined according to the dependence of the Shapiro steps on the amplitude of microwave exposure, did not exceed 50%.
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| 7. |
- Ovsyannikov, Gennady, 1948, et al.
(författare)
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Magnetic proximity effect and superconducting triplet correlations at the interface of cuprate superconductor and an oxide spin-valve
- 2016
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Ingår i: Fizika Nizkih Temperatur. - 1816-0328 .- 0132-6414. ; 42:10, s. 1115-1128
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Tidskriftsartikel (refereegranskat)abstract
- The heterostructure comprising a cuprate superconductor YBa2Cu3O7-? and a spin-valve of ruthenate/ manganite (SrRuO3/La0.7Sr0.3MnO3) has been studied by SQUID magnetometry, ferromagnetic resonance, and neutron reflectometry. It was shown that magnetic moment arises in a superconducting part of heterostructure while in spin-valve magnetic moment is suppressed. The obtained experimental value of characteristic penetration depth of magnetic moment into superconductor greatly exceeds the superconductor coherence length the cuprate superconductor indicating the dominance of mechanism of induced magnetic moment from Cu atoms. The mesa-structures made with an addition niobium superconducting electrode deposited on top of heterostructure showed superconducting current (dc Josephson effect) when thickness of interlayer was much greater than the coherence lengths of ferromagnetic materials of spin-valve. The maximum of the dependence of critical current density vs. thicknesses of magnetic materials corresponds to their coherence lengths, that is consistent with the theoretical predictions for the case of spin-triplet pairing. The superconducting current is observed at magnetic fields by two orders greater than the value of magnetic field corresponding to the occurrence of one magnetic flux quantum in the mesa-structure. The ratio of the second harmonic in current-phase relation of the superconducting current of mesa structure to the first harmonic, obtained from measurements of Shapiro step amplitudes under microwaves did not exceed 50%.
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| 8. |
- Ovsyannikov, Gennady, 1948, et al.
(författare)
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Magnetic proximity effect at the interface between a cuprate superconductor and an oxide spin valve
- 2016
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Ingår i: Journal of Experimental and Theoretical Physics. - : Pleiades Publishing Ltd. - 1090-6509 .- 1063-7761. ; 122:4, s. 738-747
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Tidskriftsartikel (refereegranskat)abstract
- A heterostructure that consists of the YBa2Cu3O7-delta cuprate superconductor and the SrRuO3/La0.7Sr0.3MnO3 ruthenate/manganite spin valve is investigated using SQUID magnetometry, ferromagnetic resonance, and neutron reflectometry. It is shown that a magnetic moment is induced due to the magnetic proximity effect in the superconducting part of the heterostructure, while the magnetic moment in the composite ferromagnetic interlayer is suppressed. The magnetization emerging in the superconductor coincides in order of magnitude with the results of calculations taking into account the induced magnetic moment of Cu atoms because of orbital reconstruction at the interface between the superconductor and the ferromagnet, as well as with the results of the model taking into account the variations in the density of states at a distance on the order of the coherence length in the superconductor. The experimentally obtained characteristic penetration depth of the magnetic moment in the superconductor considerably exceeds the coherence length of the cuprate superconductor, which indicates the predominance of the mechanism of induced magnetic moment of Cu atoms.
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| 9. |
- Ovsyannikov, Gennady, 1948, et al.
(författare)
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Proximity effect and electron transport in oxide hybrid heterostructures with superconducting/magnetic interfaces
- 2011
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 24:5, s. Art. no. 055012-
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Tidskriftsartikel (refereegranskat)abstract
- We report on electron transport in oxide heterostructures with superconducting/magnetic (S/M) thin film interfaces. The investigated hybrid mesa-heterostructures consist of a cuprate superconductor, a nonsuperconducting cuprate (antiferromagnetic) or manganite (ferromagnetic) interlayer with thickness d(M) = 5-50 nm and a conventional superconductor (Nb). The superconducting critical current (I-C) with a critical current density j(c) = 10(3) A cm(-2) (for d(M) = 10 nm) and a characteristic voltage ICRN = 100-200 mu V (RN is normal resistance) are observed at liquid helium temperature for a CaXSr1-XCuO2 antiferromagnetic cuprate interlayer with a thickness of d(M) = 10-50 nm. The superconducting current-phase relation of heterostructures deviates from the regular sine type, demonstrating a second harmonic component. These hybrid heterostructures with S/M interfaces show unusually high sensitivity to external magnetic fields. When substituting the cuprate interlayer by a manganite film, no critical current was observed although the manganite interlayer was made several times thinner (down to d(M)
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| 10. |
- Sheyerman, A. E., et al.
(författare)
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Spin-triplet electron transport in hybrid superconductor heterostructures with a composite ferromagnetic interlayer
- 2015
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Ingår i: Journal of Experimental and Theoretical Physics. - 1090-6509 .- 1063-7761. ; 120:6, s. 1024-1033
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid YBa2Cu3O7 - x /SrRuO3/La0.7Sr0.3MnO3/Au-Nb superconductor mesastructures with a composite manganite-ruthenate ferromagnetic interlayer are studied using electrophysical, magnetic, and microwave methods. The supercurrent in the mesastructure is observed when the interlayer thickness is much larger than the coherence length of ferromagnetic materials. The peak on the dependence of the critical current density on the interlayer material thickness corresponds to the coherence length, which is in qualitative agreement with theoretical predictions for a system with spit-triplet superconducting correlations. The magnetic-field dependence of the critical current is determined by penetration of magnetic flux quanta and by the magnetic domain structure, as well as by the field dependence of disorientation of the magnetization vectors of the layers in the composite magnetic interlayer. It is found that the supercurrent exists in magnetic fields two orders of magnitude stronger than the field corresponding to entry of a magnetic flux quantum into the mesastructure. The current-phase relation (CPR) of the supercurrent of mesastructures is investigated upon a change in the magnetic field from zero to 30 Oe; the ratio of the second CPR harmonic to the first, determined from the dependence of the Shapiro steps on the microwave radiation amplitude, does not exceed 50%.
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