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| 2. |
- Massarotti, D., et al.
(author)
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Hysteretic Critical State in Coplanar Josephson Junction with Monolayer Graphene Barrier
- 2017
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In: 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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Journal article (peer-reviewed)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. |
- Massarotti, D., et al.
(author)
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What happens in Josephson junctions at high critical current densities
- 2017
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In: Fizika Nizkih Temperatur. - : AIP Publishing. - 1816-0328 .- 0132-6414. ; 43:7, s. 816-823
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Journal article (peer-reviewed)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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| 4. |
- Tafuri, F., et al.
(author)
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Recent Achievements on the Physics of High-T cSuperconductor Josephson Junctions: Background, Perspectives and Inspiration
- 2013
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In: 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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Research review (peer-reviewed)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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| 5. |
- Galletti, L., et al.
(author)
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Influence of topological edge states on the properties of Al/Bi2Se3/Al hybrid Josephson devices
- 2014
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In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 89:13
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Journal article (peer-reviewed)abstract
- In superconductor-topological insulator-superconductor hybrid junctions, the barrier edge states are expected to be protected against backscattering, to generate unconventional proximity effects, and, possibly, to signal the presence of Majorana fermions. The standards of proximity modes for these types of structures have to be settled for a neat identification of possible new entities. Through a systematic and complete set of measurements of the Josephson properties we find evidence of ballistic transport in coplanar Al-Bi2Se3-Al junctions that we attribute to a coherent transport through the topological edge state. The shunting effect of the bulk only influences the normal transport. This behavior, which can be considered to some extent universal, is fairly independent of the specific features of superconducting electrodes. A comparative study of Shubnikov-de Haas oscillations and scanning tunneling spectroscopy gave an experimental signature compatible with a two-dimensional electron transport channel with a Dirac dispersion relation. A reduction of the size of the Bi2Se3 flakes to the nanoscale is an unavoidable step to drive Josephson junctions in the proper regime to detect possible distinctive features of Majorana fermions.
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| 6. |
- Galletti, L., et al.
(author)
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Josephson effect in Al/Bi2Se3/Al coplanar hybrid devices
- 2014
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In: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 503, s. 162-165
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Journal article (peer-reviewed)abstract
- The edge states of Topological Insulators (TI) are protected against backscattering, thanks to the topological properties arising from their band structure. Coupling a TI to a superconductor (S) can induce unconventional effects, including the creation of Majorana bound states (MBS). The fabrication of coplanar hybrid devices is a fundamental step to pave the way to the understanding of proximity effects in topologically non-trivial systems, and to a large variety of experiments aimed at the possible detection of MBS. We discuss the feasibility and some relevant properties of Al-Bi2Se3-Al coplanar proximity devices. Special attention is devoted to the design of the junction, aimed at enhancing the coupling between the electrodes and the TI.
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| 7. |
- Jouault, B., et al.
(author)
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Josephson Coupling in Junctions Made of Monolayer Graphene Grown on SiC
- 2016
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In: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1947 .- 1557-1939. ; 29:5, s. 1145-1150
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Journal article (peer-reviewed)abstract
- Chemical vapor deposition has proved to be successful in producing graphene samples on silicon carbide (SiC) homogeneous at the centimeter scale in terms of Hall conductance quantization. Here, we report on the realization of co-planar diffusive Al/ monolayer graphene/ Al junctions on the same graphene sheet, with separations between the electrodes down to 200 nm. Robust Josephson coupling has been measured for separations not larger than 300 nm. Transport properties are reproducible on different junctions and indicate that graphene on SiC substrates is a concrete candidate to provide scalability of hybrid Josephson graphene/superconductor devices.
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| 8. |
- Massarotti, D., et al.
(author)
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Breakdown of the escape dynamics in Josephson junctions
- 2015
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In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 92:5
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Journal article (peer-reviewed)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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| 9. |
- Massarotti, D., et al.
(author)
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Incipient Berezinskii-Kosterlitz-Thouless transition in two-dimensional coplanar Josephson junctions
- 2016
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In: Physical Review B. - 2469-9969 .- 2469-9950. ; 94:5
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Journal article (peer-reviewed)abstract
- Superconducting hybrid junctions are revealing a variety of effects. Some of them are due to the special layout of these devices, which often use a coplanar configuration with relatively large barrier channels and the possibility of hosting Pearl vortices. A Josephson junction with a quasi-ideal two-dimensional barrier has been realized by growing graphene on SiC with Al electrodes. Chemical vapor deposition offers centimeter size monolayer areas where it is possible to realize a comparative analysis of different devices with nominally the same barrier. In samples with a graphene gap below 400 nm, we have found evidence of Josephson coherence in the presence of an incipient Berezinskii-Kosterlitz-Thouless transition. When the magnetic field is cycled, a remarkable hysteretic collapse and revival of the Josephson supercurrent occurs. Similar hysteresis are found in granular systems and are usually justified within the Bean critical state model (CSM). We show that the CSM, with appropriate account for the low-dimensional geometry, can partly explain the odd features measured in these junctions.
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| 10. |
- Massarotti, V, et al.
(author)
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LiMn2O4 low-temperature phase: synchrotron and neutron diffraction study
- 1999
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In: JOURNAL OF APPLIED CRYSTALLOGRAPHY. - : MUNKSGAARD INT PUBL LTD. - 0021-8898. ; 32, s. 1186-1189
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Journal article (other academic/artistic)abstract
- The structural evolution of LiMn2O4 spinel was followed from 320 K down to 10 K. The structural transformation, recently studied down to 230 K [Rodriguez-Carvajal, Rousse, Masquelier & Hervieu (1998). Phys. Rev. Lett. 81, 4660-4663], takes place near room
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| 11. |
- Uvnäs-Moberg, Kerstin, et al.
(author)
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Maternal plasma levels of oxytocin during breastfeeding-A systematic review
- 2020
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 15:8
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Journal article (peer-reviewed)abstract
- Introduction Oxytocin is a key hormone in breastfeeding. No recent review on plasma levels of oxytocin in response to breastfeeding is available. Materials and methods Systematic literature searches on breastfeeding induced oxytocin levels were conducted 2017 and 2019 in PubMed, Scopus, CINAHL, and PsycINFO. Data on oxytocin linked effects and effects of medical interventions were included if available. Results We found 29 articles that met the inclusion criteria. All studies had an exploratory design and included 601 women. Data were extracted from the articles and summarised in tables. Breastfeeding induced an immediate and short lasting (20 minutes) release of oxytocin. The release was pulsatile early postpartum (5 pulses/10 minutes) and coalesced into a more protracted rise as lactation proceeded. Oxytocin levels were higher in multiparous versus primiparous women. The number of oxytocin pulses during early breastfeeding was associated with greater milk yield and longer duration of lactation and was reduced by stress. Breastfeeding-induced oxytocin release was associated with elevated prolactin levels; lowered ACTH and cortisol (stress hormones) and somatostatin (a gastrointestinal hormone) levels; enhanced sociability; and reduced anxiety, suggesting that oxytocin induces physiological and psychological adaptations in the mother. Mechanical breast pumping, but not bottle-feeding was associated with oxytocin and prolactin release and decreased stress levels. Emergency caesarean section reduced oxytocin and prolactin release in response to breastfeeding and also maternal mental adaptations. Epidural analgesia reduced prolactin and mental adaptation, whereas infusions of synthetic oxytocin increased prolactin and mental adaptation. Oxytocin infusion also restored negative effects induced by caesarean section and epidural analgesia. Conclusions Oxytocin is released in response to breastfeeding to cause milk ejection, and to induce physiological changes to promote milk production and psychological adaptations to facilitate motherhood. Stress and medical interventions during birth may influence these effects and thereby adversely affect the initiation of breastfeeding.
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