| 1. |
- Charpentier, Sophie, 1983, et al.
(författare)
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Induced unconventional superconductivity on the surface states of Bi2Te3 topological insulator
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Topological superconductivity is central to a variety of novel phenomena involving the interplay between topologically ordered phases and broken-symmetry states. The key ingredient is an unconventional order parameter, with an orbital component containing a chiral p(x) + ip(y) wave term. Here we present phase-sensitive measurements, based on the quantum interference in nanoscale Josephson junctions, realized by using Bi2Te3 topological insulator. We demonstrate that the induced superconductivity is unconventional and consistent with a sign-changing order parameter, such as a chiral px + ipy component. The magnetic field pattern of the junctions shows a dip at zero externally applied magnetic field, which is an incontrovertible signature of the simultaneous existence of 0 and pi coupling within the junction, inherent to a non trivial order parameter phase. The nano-textured morphology of the Bi2Te3 flakes, and the dramatic role played by thermal strain are the surprising key factors for the display of an unconventional induced order parameter.
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| 2. |
- Fülöp, Attila, 1988, et al.
(författare)
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Phase transition of bismuth telluride thin films grown by MBE
- 2014
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Ingår i: Applied Physics Express. - 1882-0786 .- 1882-0778. ; 7:4, s. Art. no. 045503-
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Tidskriftsartikel (refereegranskat)abstract
- A previously unreported phase transition between Bi2Te3 and Bi4Te3 in bismuth telluride grown by molecular beam epitaxy is recorded via XRD, AFM, and SIMS observations. This transition is found to be related to the Te/Bi beam equivalent pressure (BEP) ratio. BEP ratios below 17 favor the formation of Bi4Te3 while Bi2Te3 is formed at higher ratios. Transport measurements reveal that Bi2Te3 has higher electron mobility than Bi4Te3.
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| 3. |
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| 4. |
- galletti, luca, 1986, et al.
(författare)
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High-Transparency Al/Bi2Te3 Double-Barrier Heterostructures
- 2017
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 27:4
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated highly transparent Al/Bi2Te3/Al superconductor/normal metal/superconductor double-barrier heterostructures. Transport measurements reveal the presence of multiple Andreev reflections related to two distinct energy gaps that we identify as the induced superconducting gap in the two electrodes. The realization of high-transparency Josephson junctions with topological insulators is an important step towards the study of topological superconductivity and Majorana fermions.
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| 5. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
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Homogeneous superconductivity at the LaAlO3/SrTiO3 interface probed by nanoscale transport
- 2017
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 96:18
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Tidskriftsartikel (refereegranskat)abstract
- An interface between LaAlO3 and SrTiO3 (LAO/STO) may host two-dimensional superconductivity, strong spin-orbit coupling, and magnetic ordering. There are indications that the interfacial superconducting layer is nonhomogeneous at the nanoscale. The presence of inhomogeneities may have strong implications on the superconducting transport properties and lead to formation of weak links between superconducting regions. In this paper, we report on the temperature and magnetic field dependence of superconducting transport in single nanowires and nanorings fabricated in a LAO/STO interface. The analysis of data proves that our nanostructures behave like uniform superconducting filaments carrying a critical current close to the theoretical Ginzburg-Landau depairing limit. Furthermore, we unexpectedly find an enhancement of the critical current of LAO/STO nanowires and nanorings at low temperature when a magnetic field is applied. Our results point towards the coexistence of a homogeneous interfacial superconductivity and spatially separated magnetism at the LAO/STO interface.
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| 6. |
- Kunakova, Gunta, et al.
(författare)
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Bulk-free topological insulator Bi2Se3 nanoribbons with magnetotransport signatures of Dirac surface states
- 2018
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 10:41, s. 19595-19602
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 The Royal Society of Chemistry. Many applications of topological insulators (TIs) as well as new phenomena require devices with reduced dimensions. While much progress has been made to realize thin films of TIs with low bulk carrier densities, nanostructures have not yet been reported with similar properties, despite the fact that reduced dimensions should help diminish the contributions from bulk carriers. Here we demonstrate that Bi2Se3 nanoribbons, grown by a simple catalyst-free physical-vapour deposition, have inherently low bulk carrier densities, and can be further made bulk-free by thickness reduction, thus revealing the high mobility topological surface states. Magnetotransport and Hall conductance measurements, in single nanoribbons, show that at thicknesses below 30 nm, the bulk transport is completely suppressed which is supported by self-consistent band-bending calculations. The results highlight the importance of material growth and geometrical confinement to properly exploit the unique properties of topological surface states.
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| 7. |
- 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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| 8. |
- Song, Yuxin, 1981, et al.
(författare)
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MBE growth of Bi2Te3 for Thermoelectrics
- 2013
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Ingår i: Asia Communications and Photonics Conference, ACP. - Washington, D.C. : OSA. - 2162-108X.
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Konferensbidrag (refereegranskat)abstract
- Molecular beam epitaxy of Bi2Te3 on various substrates for thermoelectric applications is investigated. Growth conditions were optimized based on Si(111) substrates with two different growth techniques, co-deposition followed by crystallization and direct growth. Growth of Bi 2Te3 on GaAs, GaN, et. al. substrates with different crystal directions and offcut angles were investigated. High quality Bi2Te3 thin films were achieved with very low carrier density and record high carrier mobility.
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