| 1. |
- Ekström, Erik, et al.
(författare)
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Single-Phase Growth, Stabilization, and Electrical Properties of B Phase VO2 Films Grown on Mica by Reactive Magnetron Sputtering
- 2023
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Ingår i: ADVANCED PHYSICS RESEARCH. - : WILEY. - 2751-1200. ; 2:12
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Tidskriftsartikel (refereegranskat)abstract
- The VO2 metastable (B) phase is of interest for applications in temperature sensing, bolometry, and Li-ion batteries. However, single-phase growth of thin films of this metastable phase is a challenge because vanadium oxide exhibits many polymorphs and the VO2 stable (M1) phase is usually present as a secondary phase. Additionally, the phase transition at 350 degrees C in the (B) phase severely narrows the processing window for achieving phase-pure films. Here, single-phase growth of 5-to 50-nm thick VO2 (B) films on muscovite, mica, by pulsed direct-current reactive magnetron sputtering at 400 degrees C is demonstrated. The films are phase-pure and exhibit a high density of 4.05 g cm(-3) and low resistivity of about 50 m Omega cm at 30 degrees C. Increasing the film thickness to 100 nm results in a V2O5-capped VO2 (B) film with a resistivity of 8000 m Omega cm. These results indicate that the stability of the VO2 (B) phase is sensitive to in situ annealing during deposition. These findings should serve as a basis to design processes to exclusively obtain phase-pure VO2 (B) films.
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| 2. |
- Jouan, A., et al.
(författare)
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Multiband Effects in the Superconducting Phase Diagram of Oxide Interfaces
- 2022
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Ingår i: Advanced Materials Interfaces. - : Wiley. - 2196-7350. ; 9:29
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Tidskriftsartikel (refereegranskat)abstract
- A dome-shaped phase diagram of superconducting critical temperature upon doping is often considered as a hallmark of unconventional superconductors. This behavior, observed in SrTiO3-based interfaces, whose electronic density is controlled by field-effect, has not been explained unambiguously yet. Here, a generic scenario for the superconducting phase diagram of these oxide interfaces is elaborated based on transport experiments on a double-gate LaAlO3/SrTiO3 field-effect device and Schrödinger–Poisson numerical simulations of the quantum well. The optimal doping point of maximum Tc is ascribed to the transition between a single-gap and a fragile two-gap s±-wave superconducting state involving bands of different orbital character. Close to this point, a bifurcation in the dependence of Tc on the carrier density, which can be controlled by the details of the doping execution, is observed experimentally and reproduced by numerical simulations. Where doping with a back-gate triggers the filling of a new (Formula presented.) subband and initiates the overdoped regime, doping with a top-gate delays the filling of the subband and maintains the 2D electron gaz in the single-gap state of higher Tc. Such a bifurcation, whose branches can be followed reversibly, provides a generic explanation for the dome-shaped superconducting phase diagram that could be extended to other multiband superconducting materials.
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| 3. |
- 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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