| 1. |
- Andzane, J., et al.
(författare)
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Catalyst-free vapour-solid technique for deposition of Bi2Te3 and Bi2Se3 nanowires/nanobelts with topological insulator properties
- 2015
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 7:38, s. 15935-15944
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Tidskriftsartikel (refereegranskat)abstract
- We present a simple two-stage vapour-solid synthesis method for the growth of bismuth chalcogenide (Bi2Te3, Bi2Se3) topological insulator nanowires/nanobelts by using Bi2Se3 or Bi2Te3 powders as source materials. During the first stage of the synthesis process nanoplateteles, serving as "catalysts" for further nanowire/nanobelt growth, are formed. At a second stage of the synthesis, the introduction of a N-2 flow at 35 Torr pressure in the chamber induces the formation of free standing nanowires/nanobelts. The synthesised nanostructures demonstrate a layered single-crystalline structure and Bi : Se and Bi : Te ratios 40 : 60 at% for both Bi2Se3 and Bi2Te3 nanowires/nanobelts. The presence of Shubnikov de Haas oscillations in the longitudinal magneto-resistance of the nanowires/nanobelts and their specific angular dependence confirms the existence of 2D topological surface states in the synthesised nanostructures.
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| 2. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Resistive state triggered by vortex entry in YBa2Cu3O7-delta nanostructures
- 2014
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 506, s. 165-168
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Tidskriftsartikel (refereegranskat)abstract
- We have realized YBa2Cu3O7-delta nanowires and nano Superconducting Quantum Interference Devices (nanoSQUID). The measured temperature dependence of the wire resistances below the superconducting transition temperature has been analyzed using a thermally activated vortex entry model valid for wires wider than the superconducting coherence length. The extracted zero temperature values of the London penetration depth, lambda(0) similar or equal to 270 +/- 15 nm, are in good agreement with the value obtained from critical current modulations as a function of an externally applied magnetic field in a nanoSQUID implementing two nanowires.
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| 3. |
- 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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| 4. |
- Kunakova, Gunta, 1987, et al.
(författare)
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High-Mobility Ambipolar Magnetotransport in Topological Insulator Bi2Se3 Nanoribbons
- 2021
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Ingår i: Physical Review Applied. - 2331-7019. ; 16:2
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Tidskriftsartikel (refereegranskat)abstract
- Nanoribbons of topological insulators (TIs) have been suggested for a variety of applications exploiting the properties of the topologically protected surface Dirac states. In these proposals it is crucial to achieve a high tunability of the Fermi energy, through the Dirac point while preserving a high mobility of the involved carriers. Tunable transport in TI nanoribbons has been achieved by chemical doping of the materials so to reduce the bulk carriers' concentration, however at the expense of the mobility of the surface Dirac electrons, which is substantially reduced. Here we study bare Bi2Se3 nanoribbons transferred on a variety of oxide substrates and demonstrate that the use of a large relative permittivity SrTiO3 substrate enables the Fermi energy to be tuned through the Dirac point and an ambipolar field effect to be obtained. Through magnetotransport and Hall conductance measurements, performed on single Bi2Se3 nanoribbons, we demonstrate that electron and hole carriers are exclusively high-mobility Dirac electrons, without any bulk contribution. The use of SrTiO3 allows therefore an easy field effect gating in TI nanostructures providing an ideal platform to take advantage of the properties of topological surface states.
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| 5. |
- Kunakova, Gunta, 1987, et al.
(författare)
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High transparency Bi 2 Se 3 topological insulator nanoribbon Josephson junctions with low resistive noise properties
- 2019
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 115:17
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Tidskriftsartikel (refereegranskat)abstract
- Bi2Se3 nanoribbons, grown by catalyst-free Physical Vapor Deposition, have been used to fabricate high quality Josephson junctions with Al superconducting electrodes. The conductance spectra (dI/dV) of the junctions show clear dip-peak structures characteristic of multiple Andreev reflections. The temperature dependence of the dip-peak features reveals a highly transparent Al/Bi2Se3 topological insulator nanoribbon interface and Josephson junction barrier. This is supported by the high values of the Bi2Se3 induced gap and of IcRn (where Ic is the critical current and Rn is the normal resistance of the junction) product both of the order of 160 μeV, a value close to the Al gap. The devices present an extremely low relative resistance noise below 1 × 10-12 μm2/Hz comparable to the best Al tunnel junctions, which indicates a high stability in the transmission coefficients of transport channels. The ideal Al/Bi2Se3 interface properties, perfect transparency for Cooper pair transport in conjunction with low resistive noise, make these junctions a suitable platform for further studies of the induced topological superconductivity and Majorana bound states physics.
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| 6. |
- Kunakova, Gunta, 1987, et al.
(författare)
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Space charge limited current mechanism in Bi2S3 nanowires
- 2016
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 119:11
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Tidskriftsartikel (refereegranskat)abstract
- We report on the charge transport properties of individual Bi2S3 nanowires grown within the pores of anodized aluminum oxide templates. The mean pore diameter was 80 nm. Space charge limited current is the dominating conduction mechanism at temperatures below 160 K. Characteristic parameters of nanowires, such as trap concentration and trap characteristic energy, were estimated from current-voltage characteristics at several temperatures.
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| 7. |
- Kunakova, Gunta, 1987, et al.
(författare)
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Topological insulator nanoribbon Josephson junctions: Evidence for size effects in transport properties
- 2020
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 128:19
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Tidskriftsartikel (refereegranskat)abstract
- We have used Bi 2 Se 3 nanoribbons, grown by catalyst-free physical vapor deposition to fabricate high quality Josephson junctions with Al superconducting electrodes. In our devices, we observe a pronounced reduction of the Josephson critical current density J c by reducing the width of the junction, which in our case corresponds to the width of the nanoribbon. Because the topological surface states extend over the entire circumference of the nanoribbon, the superconducting transport associated with them is carried by modes on both the top and bottom surfaces of the nanoribbon. We show that the J c reduction as a function of the nanoribbon width can be accounted for by assuming that only the modes traveling on the top surface contribute to the Josephson transport as we derive by geometrical consideration. This finding is of great relevance for topological quantum circuitry schemes since it indicates that the Josephson current is mainly carried by the topological surface states.
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| 8. |
- Pullukattuthara Surendran, Ananthu, 1994, et al.
(författare)
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Current-phase relation of a short multi-mode Bi 2 Se 3 topological insulator nanoribbon Josephson junction with ballistic transport modes
- 2023
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Ingår i: Superconductor Science and Technology. - 0953-2048 .- 1361-6668. ; 36:6
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Tidskriftsartikel (refereegranskat)abstract
- We used the asymmetric superconducting quantum interference device (SQUID) technique to extract the current phase relation (CPR) of a Josephson junction with a 3D-topological insulator (3D-TI) Bi2Se3 nanobelt as the barrier. The obtained CPR shows deviations from the standard sinusoidal CPR with a pronounced forward skewness. At temperatures below 200 mK, the junction skewness values are above the zero temperature limit for short diffusive junctions. Fitting of the extracted CPR shows that most of the supercurrent is carried by ballistic topological surface states (TSSs), with a small contribution of diffusive channels primarily due to the bulk. These findings are instrumental in engineering devices that can fully exploit the properties of the topologically protected surface states of 3D TIs.
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| 9. |
- Salvato, Matteo, et al.
(författare)
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Nanometric Moire Stripes on the Surface of Bi2Se3 Topological Insulator
- 2022
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 16:9, s. 13860-13868
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Tidskriftsartikel (refereegranskat)abstract
- Mismatch between adjacent atomic layers in low-dimensional materials, generating moire patterns, has recently emerged as a suitable method to tune electronic properties by inducing strong electron correlations and generating novel phenomena. Beyond graphene, van der Waals structures such as three-dimensional (3D) topological insulators (TIs) appear as ideal candidates for the study of these phenomena due to the weak coupling between layers. Here we discover and investigate the origin of 1D moire stripes on the surface of Bi2Se3 TI thin films and nanobelts. Scanning tunneling microscopy and high-resolution transmission electron microscopy reveal a unidirectional strained top layer, in the range 14-25%, with respect to the relaxed bulk structure, which cannot be ascribed to the mismatch with the substrate lattice but rather to strain induced by a specific growth mechanism. The 1D stripes are characterized by a spatial modulation of the local density of states, which is strongly enhanced compared to the bulk system. Density functional theory calculations confirm the experimental findings, showing that the TI surface Dirac cone is preserved in the 1D moire stripes, as expected from the topology, though with a heavily renormalized Fermi velocity that also changes between the top and valley of the stripes. The strongly enhanced density of surface states in the TI 1D moire superstructure can be instrumental in promoting strong correlations in the topological surface states, which can be responsible for surface magnetism and topological superconductivity.
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