| 1. |
- Massarotti, D., et al.
(författare)
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Breakdown of the escape dynamics in Josephson junctions
- 2015
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 92:5
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Tidskriftsartikel (refereegranskat)abstract
- We have identified anomalous behavior of the escape rate out of the zero-voltage state in Josephson junctions with a high critical current density J(c). For this study we have employed YBa2Cu3O7-x grain boundary junctions, which span a wide range of J(c) and have appropriate electrodynamical parameters. Such high Jc junctions, when hysteretic, do not switch from the superconducting to the normal state following the expected stochastic Josephson distribution, despite having standard Josephson properties such as a Fraunhofer magnetic field pattern. The switching current distributions (SCDs) are consistent with nonequilibrium dynamics taking place on a local rather than a global scale. This means that macroscopic quantum phenomena seem to be practically unattainable for high Jc junctions. We argue that SCDs are an accurate means to measure nonequilibrium effects. This transition from global to local dynamics is of relevance for all kinds of weak links, including the emergent family of nanohybrid Josephson junctions. Therefore caution should be applied in the use of such junctions in, for instance, the search for Majorana fermions.
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| 2. |
- Massarotti, D., et al.
(författare)
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Hysteretic Critical State in Coplanar Josephson Junction with Monolayer Graphene Barrier
- 2017
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Ingår i: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1947 .- 1557-1939. ; 30:1, s. 5-14
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Tidskriftsartikel (refereegranskat)abstract
- Coplanar Al/graphene/Al junctions fabricated on the same graphene sheet deposited on silicon carbide (SiC), show robust Josephson coupling at subKelvin temperature, when the separations between the electrodes is below 400 nm. Remarkably, a hysteretic Critical State sets in when ramping an orthogonal magnetic field, with a sudden collapse of the Josephson critical current I (c) when turning the field on, and a revival of I (c) when inverting the sweep. Similar hysteresis can be found in granular superconducting films which may undergo the Berezinskii-Kosterlitz-Thouless transition. Here, we give quantitative arguments to prove that this odd behavior of the magnetoconductance gives evidence for an incipient Berezinskii-Kosterlitz-Thouless transition with drift and pinning of fluctuating free vortices induced by the current bias.
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| 3. |
- Stornaiuolo, D., et al.
(författare)
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Advances in YBa2Cu3O7-delta grain boundary biepitaxial Josephson junctions: Transport properties and mesoscopic effects
- 2007
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 17:2, s. 225-228
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Tidskriftsartikel (refereegranskat)abstract
- We report on the latest developments in the study of transport properties of YBa2CU3O7-delta (YBCO)-based grain boundary (GB) biepitaxial Josephson junctions. We have successfully extended the fabrication process s,. originally developed for (110) oriented SrTiO3 substrates, to (110) oriented LaAlO3 substrates in view of microwave applications. We will report, also, on the observation of conductance fluctuations, we believe related to the coherent diffusion of quasi-particles across the GB. These results, together with the recent observation of macroscopic quantum tunneling and energy level quantization in these Junctions, could help cast some light on the mechanism involved in transport across grain boundaries and in revising the role and the effect of quasi particles in d-wave transport.
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| 4. |
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| 5. |
- Tafuri, F., et al.
(författare)
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Coherent quasiparticle transport in grain boundary junctions employing high-T-c superconductors
- 2006
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Ingår i: Microelectronics. - : Elsevier BV. - 0026-2692. ; 39:8, s. 1066-1069
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Konferensbidrag (refereegranskat)abstract
- Magneto-fluctuations of the normal resistance R-N have been reproducibly observed in YBa2Cu3O7-delta biepitaxial grain boundary junctions at low temperatures. We attribute them to mesoscopic transport in narrow channels across the grain boundary line, occurring even in the presence of large voltage drops. The Thouless energy appears to be the relevant energy scale. Possible implications on the understanding of coherent transport of quasiparticles in high critical temperature superconductors (HTS) and of the dissipation mechanisms are discussed. (c) 2007 Elsevier Ltd. All rights reserved.
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| 6. |
- Tafuri, F., et al.
(författare)
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Mesoscopic conductance fluctuations in high-T-c grain boundary Josephson junctions: Coherent quasiparticle transport
- 2007
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 460-462:Part 1, s. 343-346
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Tidskriftsartikel (refereegranskat)abstract
- Magneto-fluctuations of the normal resistance RN have been reproducibly observed in YBa2Cu3O7-delta (HTS) biepitaxial grain boundary junctions at low temperatures. We attribute them to mesoscopic transport in narrow channels across the grain boundary line. The Thouless energy appears to be the relevant energy scale. Possible implications on the understanding of coherent transport of quasiparticles in HTS and of the dissipation mechanisms are discussed. (c) 2007 Elsevier B.V. All rights reserved.
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| 7. |
- Tafuri, Francesco, et al.
(författare)
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Quantum behaviors in high-T-c systems: Macroscopic and vortex quantum tunneling
- 2006
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 437-38:SPEC. ISS., s. 303-308
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Konferensbidrag (refereegranskat)abstract
- We describe the main ideas and some experimental outcomes of two experiments, both aimed to study quantum tunneling effects in high-T C structures. In the first experiment, macroscopic quantum tunneling is demonstrated in grain boundary YBaCuO Josephson junctions revealing dissipation levels lower than expected and opening novel perspectives for quantum circuitry. In the second, the low temperature dissipation is dominated by quantum tunneling of individual Pearl vortices in ultra-thin CaBaCuO systems characterized by extremely long Pearl lengths. © 2006 Elsevier B.V. All rights reserved.
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| 8. |
- Tafuri, F., et al.
(författare)
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Recent Achievements on the Physics of High-T cSuperconductor Josephson Junctions: Background, Perspectives and Inspiration
- 2013
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Ingår i: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1947 .- 1557-1939. ; 26:1, s. 21-41
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Forskningsöversikt (refereegranskat)abstract
- Coherent passage of Cooper pairs in a Josephson junction (JJ) above the liquid nitrogen temperature has been the first impressive revolutionary effect induced by high critical temperature superconductors (HTS) in the domain of the study of Josephson effect (JE). But this has been only the start. A d-wave order parameter has lead to significant novel insights in the physics of the JE turning into a device the notion of a pi-junction. Spontaneous currents in a frustrated geometry, Andreev bound states, long-range proximity effect have rapidly become standard terms in the study of the JE, standing as a reference bench for conventional systems based on low critical temperature superconductors (LTS) and inspiring analogies for junctions based on novel superconductors discovered in the meantime. The extreme richness of the physics of HTS JJs has not been adequately supported by the expected impact in the applications, the main reason lying in the complexity of these materials and in the consequent unsatisfactory yield and reproducibility of the performances of the JJs within the required limits. The continuous progress in material science, and specifically in the realization of oxide multi-layers, and in nanotechnologies applied to superconductors, accompanied by the advances in a better understanding of the properties of HTS and of HTS devices, has as a matter of fact opened possible novel scenarios and interest in the field. We intend to give a brief overview on interesting new problems concerning HTS JJs of inspiration also for other systems. We also review some ideas and experimental techniques on macroscopic quantum decay phenomena occurring in Josephson structures. The attention is mainly addressed to intermediate levels of dissipation, which characterize a large majority of low critical current Josephson devices and are therefore an unavoidable consequence of nanotechnology applied more and more to Josephson devices.
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| 9. |
- Tagliacozzo, A., et al.
(författare)
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Observation of mesoscopic conductance fluctuations in YBa2Cu3O7-delta grain boundary Josephson junctions
- 2007
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 75:1, s. 012507-
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Tidskriftsartikel (refereegranskat)abstract
- Magnetofluctuations of the normal-state resistance R-N have been reproducibly observed in high-critical-temperature superconductor (HTS) grain boundary junctions at low temperatures. We attribute them to mesoscopic transport in narrow channels across the grain boundary line. The Thouless energy appears to be the relevant energy scale. Our findings have significant implications for quasiparticle relaxation and coherent transport in HTS grain boundaries.
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| 10. |
- Barthelemy, A., et al.
(författare)
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Quasi-two-dimensional electron gas at the oxide interfaces for topological quantum physics
- 2021
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 133:1
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Tidskriftsartikel (refereegranskat)abstract
- The development of “fault-tolerant” quantum computers, unaffected by noise and decoherence, is one of the fundamental challenges in quantum technology. One of the approaches currently followed is the realization of “topologically protected” qubits which make use of quantum systems characterized by a degenerate ground state of composite particles, known as “non-Abelian anyons”, able to encode and manipulate quantum information in a non-local manner. In this paper, we discuss the potential of quasi-two-dimensional electron gas (q2DEG) at the interface between band insulating oxides, like LaAlO3 and SrTiO3, as an innovative technological platform for the realization of topological quantum systems. Being characterized by a unique combination of unconventional spin-orbit coupling, magnetism, and 2D-superconductivity, these systems naturally possess most of the fundamental characteristics needed for the realization of a topological superconductor. These properties can be widely tuned by electric field effect acting on the orbital splitting and occupation of the non-degenerate 3dxy and 3dxz,yz bands. The topological state in oxide q2DEGs quasi-one-dimensional nanochannels could be therefore suitably controlled, leading to conceptual new methods for the realization of a topological quantum electronics based on the tuning of the orbital degrees of freedom.
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| 11. |
- Born, D., et al.
(författare)
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CaBaCuO ultrathin films and junctions
- 2007
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 17:2/3, s. 3581-3584
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Tidskriftsartikel (refereegranskat)abstract
- We investigated transport properties of ultrathin CaBaCuO (CBCO) bridges, focusing on vortex dynamics, and Josephson bicrystal junctions. The CBCO films used are composed of a stacking sequence of two structural subunits having different functions, namely a Ba-based charge reservoir (CR) block and a Ca-based infinite layer (IL) superconducting block. SQUID microscopy investigations of these films provide Pearl lengths A more than the bridge widths. Measuring current-voltage characteristics we found evidence that at high temperatures the vortices are thermally activated at the edge of the bridge and pushed in, causing dissipation and a power-law dependence of the voltage from the current. At lower temperatures, the experimental curves change their shape. We compared these data with the predicted behavior for vortex quantum tunneling and we found very good agreement. Moreover, we have realized Josephson junctions composed of only a few superconducting CuO2 planes. The CBCO films used in these experiments are only 8 nm thick and have six superconducting CUO2 planes. The simple structure of the GB allows a reliable estimation of the coupling along the ab planes of the CuO2. We calculate for 24 degrees symmetric and asymmetric cases a critical current density per plane of about (1-3) kA/cm(2).
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| 12. |
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| 13. |
- Fittipaldi, R., et al.
(författare)
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Superconductivity in Sr2RuO4-Sr3Ru2O7 eutectic crystals
- 2008
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 83:2, s. Art. no. 27007-
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Tidskriftsartikel (refereegranskat)abstract
- Superconducting behavior has been observed in the Sr2RuO4-Sr3Ru2O7 eutectic system as grown by the flux-feeding floating-zone technique. A supercurrent flows across a single interface between Sr2RuO4 and Sr3Ru2O7 areas at distances that are far beyond those expected in a conventional proximity effect. The current-voltage characteristics within the Sr3Ru2O7 macrodomain, as extracted from the eutectic, exhibit signatures of superconductivity in the bilayered Sr3Ru2O7 region. Detailed microstructural, morphological and compositional analyses address issues on the concentration and the size of Sr2RuO4 inclusions within the Sr3Ru2O7 matrix. We speculate on the possibility of inhomogeneous superconductivity in the eutectic Sr3Ru2O7 and exotic pairing induced by the Sr2RuO4 inclusions. Copyright (C) EPLA, 2008.
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| 14. |
- Jouan, A., et al.
(författare)
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Quantized conductance in a one-dimensional ballistic oxide nanodevice
- 2020
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Ingår i: Nature Electronics. - : Springer Science and Business Media LLC. - 2520-1131. ; 3:4, s. 201-206
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Tidskriftsartikel (refereegranskat)abstract
- The electric-field effect control of two-dimensional electron gases (2-DEGs) has allowed nanoscale electron quantum transport to be explored in semiconductors. Structures based on transition metal oxides have electronic states that favour the emergence of novel quantum orders that are absent in conventional semiconductors and the 2-DEG formed at a LaAlO3/SrTiO3 interface-a structure in which superconductivity and spin-orbit coupling can coexist-is a promising platform to develop devices for spintronics and topological electronics. However, field-effect control of the properties of this interface at the nanoscale remains challenging. Here we show that a quantum point contact can be formed in a LaAlO3/SrTiO3 interface through electrostatic confinement of the 2-DEG using a split gate. Our device exhibits a quantized conductance due to ballistic transport in a controllable number of one-dimensional conducting channels. Under a magnetic field, the direct observation of the Zeeman splitting between spin-polarized bands allows the determination of the Lande g-factor, whose value differs strongly from that of the free electrons. Through source-drain voltage measurements, we also performed a spectroscopic investigation of the 3d energy levels inside the quantum point contact. The LaAlO3/SrTiO3 quantum point contact could potentially be used as a spectrometer to probe Majorana states in an oxide 2-DEG. A quantum point contact formed in the two-dimensional electron gas of a LaAlO3/SrTiO3 interface exhibits quantized conductance due to ballistic transport in a controllable number of one-dimensional conducting channels.
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| 15. |
- Longobardi, L., et al.
(författare)
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Direct Transition from Quantum Escape to a Phase Diffusion Regime in YBaCuO Biepitaxial Josephson Junctions
- 2012
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 109:5
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Tidskriftsartikel (refereegranskat)abstract
- Dissipation encodes the interaction of a quantum system with the environment and regulates the activation regimes of a Brownian particle. We have engineered grain boundary biepitaxial YBaCuO junctions to drive a direct transition from a quantum activated running state to a phase diffusion regime. The crossover to the quantum regime is tuned by the magnetic field and dissipation is described by a fully consistent set of junction parameters. To unravel phase dynamics in moderately damped systems is of general interest for advances in the comprehension of retrapping phenomena and in view of quantum hybrid technology.
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| 16. |
- Massarotti, D., et al.
(författare)
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What happens in Josephson junctions at high critical current densities
- 2017
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Ingår i: Fizika Nizkih Temperatur. - : AIP Publishing. - 1816-0328 .- 0132-6414. ; 43:7, s. 816-823
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Tidskriftsartikel (refereegranskat)abstract
- The impressive advances in material science and nanotechnology are more and more promoting the use of exotic barriers and/or superconductors, thus paving the way to new families of Josephson junctions. Semiconducting, ferromagnetic, topological insulator and graphene barriers are leading to unconventional and anomalous aspects of the Josephson coupling, which might be useful to respond to some issues on key problems of solid state physics. However, the complexity of the layout and of the competing physical processes occurring in the junctions is posing novel questions on the interpretation of their phenomenology. We classify some significant behaviors of hybrid and unconventional junctions in terms of their first imprinting, i.e. current-voltage curves, and propose a phenomenological approach to describe some features of junctions characterized by relatively high critical current densities Jc. Accurate arguments on the distribution of switching currents will provide quantitative criteria to understand physical processes occurring in high-Jc junctions. These notions are universal and apply to all kinds of junctions. PACS: 74.72.-h Cuprate superconductors; 85.25.Cp Josephson devices; 74.50.+r Tunneling phenomena; Josephson effects.
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| 17. |
- Rotoli, G., et al.
(författare)
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Eck-Like Resonances in High-T-c Long Faceted Josephson Junctions
- 2009
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 19:3, s. 911-915
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Tidskriftsartikel (refereegranskat)abstract
- By means of numerical simulations we study the dynamics of the phase difference in faceted long Josephson junctions. We compare our simulations with experiments on a sample of high quality high-Tc biepitaxial junctions. Adjusting junction length and dissipation to reproduce the observed data we found a significant agreement, which permits to identify the observed resonances mostly as Eck steps. Some considerations are also made on the requirements to observe flux-flow or Fiske resonances in these junctions.
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| 18. |
- Stornaiuolo, D., et al.
(författare)
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Fabrication and properties of sub-micrometric YBCO biepitaxial junctions
- 2009
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 150:5
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Konferensbidrag (refereegranskat)abstract
- We report on the fabrication procedure and the transport properties of submicron grain boundary biepitaxial YBCO Josephson junctions. These first results are very encouraging and justify further expectations on improved performances for such types of devices. A reduced and more controlled faceting along the grain boundary interface, for instance, will better preserve intrinsic d-wave effects, and favour the study of fluxons dynamics.
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| 19. |
- Stornaiuolo, D, et al.
(författare)
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Sub-Micron YBa2Cu3O7-x Biepitaxial Junctions
- 2009
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 19:3, s. 174-177
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication and properties of sub-micron YBa2Cu3O7-x off-axis biepitaxial junctions. The vision behind this work is to set up a reliable nanotechnology processing to improve junctions' performances and reproducibility through the reduction of their size. We will illustrate the fabrication procedure employed and show the results obtained on samples where the transport parameters were tuned in a predictable way. Also, proofs of a clean barrier structure with few facets and low disorder were obtained.
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| 20. |
- Stornaiuolo, D., et al.
(författare)
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Submicron YBaCuO biepitaxial Josephson junctions: d-wave effects and phase dynamics
- 2010
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 107:11
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Tidskriftsartikel (refereegranskat)abstract
- We report a systematic study of the transport properties of high critical temperature superconductor (HTS) biepitaxial Josephson junctions in the submicron range. Junction performances point to more uniform and reproducible devices and to better control of d-wave intrinsic properties. Outcomes promote novel insights into the transport mechanisms across grain boundaries and encourage further developments in the control of dissipation in HTS devices. The application of nanotechnology to HTS could be an additional tool to properly engineer the junction properties to match specific circuit design also in view of the integration into hybrid quantum circuits. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3388035]
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| 21. |
- Tagliacozzo, A., et al.
(författare)
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Mesoscopic conductance fluctuations in YBa2Cu3O7-delta grain boundary junctions at low temperature
- 2009
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 79:2
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Tidskriftsartikel (refereegranskat)abstract
- The magnetoconductance in YBa2Cu3O7-delta grain boundary Josephson junctions displays fluctuations at low temperatures of mesoscopic origin. The morphology of the junction suggests that transport occurs in narrow channels across the grain boundary line with a large Thouless energy. Nevertheless the measured fluctuation amplitude decreases quite slowly when increasing the voltage up to values about 20 times the Thouless energy, of the order of the nominal superconducting gap. Our findings show the coexistence of supercurrent and quasiparticle current in the junction conduction even at high nonequilibrium conditions. Model calculations confirm the reduced role of quasiparticle relaxation at temperatures up to 3 K.
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| 22. |
- D'Antuono, M., et al.
(författare)
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Nanopatterning of oxide 2-dimensional electron systems using low-temperature ion milling
- 2022
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Ingår i: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 33:8
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Tidskriftsartikel (refereegranskat)abstract
- We present a 'top-down' patterning technique based on ion milling performed at low-temperature, for the realization of oxide two-dimensional electron system devices with dimensions down to 160 nm. Using electrical transport and scanning Superconducting QUantum Interference Device measurements we demonstrate that the low-temperature ion milling process does not damage the 2DES properties nor creates oxygen vacancies-related conducting paths in the STO substrate. As opposed to other procedures used to realize oxide 2DES devices, the one we propose gives lateral access to the 2DES along the in-plane directions, finally opening the way to coupling with other materials, including superconductors.
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| 23. |
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| 24. |
- Rotoli, G., et al.
(författare)
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Resonant phase dynamics in 0-π Sine–Gordon facets
- 2015
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer Science and Business Media LLC. - 0935-1175 .- 1432-0959. ; 27:4-5, s. 639-658
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Tidskriftsartikel (refereegranskat)abstract
- A locally phase-shifted Sine–Gordon model well accounts for the phenomenology of unconventional Josephson junctions. The phase dynamics shows resonant modes similar to Fiske modes that appear both in the presence and in the absence of the external magnetic field in standard junctions. In the latter case, they are also in competition with zero field propagation of Sine–Gordon solitons, i.e., fluxons, which give rise to the so-called zero field steps in the current–voltage (I–V) of the junction. We numerically study the I–V characteristics and the resonances magnetic field patterns for some different faceting configurations, in various dissipative regimes, as a function of temperature. The simulated dynamics of the phase is analyzed for lower-order resonances. We give evidence of a nontrivial dynamics due to the interaction of propagating fluxons with localized semifluxons. Numerical results are compared with experimental outcomes obtained on high-quality high-Tc grain boundary YBCO junctions.
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