| 1. |
- Andersson, Eric, 1992, et al.
(author)
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Fabrication and electrical transport characterization of high quality underdoped YBa2Cu3O7-δ nanowires
- 2020
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In: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 33:6
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Journal article (peer-reviewed)abstract
- We present the fabrication and electrical transport characterization of underdoped YBa2Cu3O7-δnanowires. The nanowires have been realized without any protective capping layer and theyshow transport properties similar to those of the parent thin film, demonstrating that they havenot been damaged by the nanopatterning. The current-voltage characteristics of the underdopednanowires show large hysteretic voltage switching at the critical current, in contrast to theflux-flow like characteristics of optimally doped nanostructures, indicating the formation of aself-stabilizing hot spot. These results open up new possibilities for using the underdopednanowires as single photon detectors and for exploring the underdoped side of the YBa2Cu3O7-δphase diagram at the nanoscale.
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| 2. |
- Andersson, Eric, et al.
(author)
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Generating semantic graph corpora with graph expansion grammar
- 2023
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In: 13th International Workshop on Non-Classical Models of Automata and Applications (NCMA 2023). - : Open Publishing Association. ; , s. 3-15
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Conference paper (peer-reviewed)abstract
- We introduce LOVELACE, a tool for creating corpora of semantic graphs.The system uses graph expansion grammar as a representational language, thus allowing users to craft a grammar that describes a corpus with desired properties. When given such grammar as input, the system generates a set of output graphs that are well-formed according to the grammar, i.e., a graph bank.The generation process can be controlled via a number of configurable parameters that allow the user to, for example, specify a range of desired output graph sizes.Central use cases are the creation of synthetic data to augment existing corpora, and as a pedagogical tool for teaching formal language theory.
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| 3. |
- Andersson, Eric, 1992, et al.
(author)
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Nondestructive cleaning of the LaAlO3/SrTiO3 surface with ultraviolet light and ozone
- 2016
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In: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics. - : American Vacuum Society. - 2166-2746 .- 2166-2754. ; 34:4
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Journal article (peer-reviewed)abstract
- The effect of ultraviolet light produced ozone and irradiation (UV/ozone) cleaning on the surface properties and interface electrical properties of 4 unit cell (uc) LaAlO3/SrTiO3 samples is examined. A standard photolithography process is used to contaminate the samples which are then cleaned in UV/ozone. Atomic force microscopy measurements show that the photoresist contaminated samples can be cleaned efficiently using this method. The surface roughness of the cleaned samples is comparable to that of the as-grown samples. Furthermore, electrical transport measurements show that the mobility decreases and the sheet carrier density increases for the contaminated samples, which also display indications of an onset to the Kondo effect. By removing the contaminants with UV/ozone cleaning, the mobility and sheet carrier density can be partially restored toward the as-grown values. The mobility is increased by about two times from approximate to 1000 cm(2) V-1 s(-1) for the contaminated samples to approximate to 2000 cm(2) V-1 s(-1) for the ozone cleaned ones. (C) 2016 American Vacuum Society.
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| 4. |
- Arpaia, Riccardo, 1985, et al.
(author)
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Dynamical charge density fluctuations pervading the phase diagram of a Cu-based high-Tc superconductor
- 2019
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 365:6456, s. 906-910
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Journal article (peer-reviewed)abstract
- Charge density modulations have been observed in all families of high–critical temperature (Tc) superconducting cuprates. Although they are consistently found in the underdoped region of the phase diagram and at relatively low temperatures, it is still unclear to what extent they influence the unusual properties of these systems. Using resonant x-ray scattering, we carefully determined the temperature dependence of charge density modulations in YBa2Cu3O7–d and Nd1+xBa2–xCu3O7–d for several doping levels. We isolated short-range dynamical charge density fluctuations in addition to the previously known quasi-critical charge density waves. They persist up to well above the pseudogap temperature T*, are characterized by energies of a few milli–electron volts, and pervade a large area of the phase diagram.
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| 5. |
- Arpaia, Riccardo, 1985, et al.
(author)
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Probing the phase diagram of cuprates with YBa2Cu3O7−δ thin films and nanowires
- 2018
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In: Physical Review Materials. - 2475-9953. ; 2:2
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Journal article (peer-reviewed)abstract
- We have grown and characterized 30-nm-thick YBa2Cu3O7−δ (YBCO) films, deposited by pulsed laser deposition on both MgO (110) and SrTiO3 (001) substrates, which induce opposite strain to the superconducting layer. By carefully tuning the in situ post-annealing oxygen pressure, we achieved, in a reproducible way, films at different oxygen doping, spanning from the slightly overdoped down to the strongly underdoped region of the phase diagram. The transport properties of the films, investigated through resistance versus temperature measurements, are in perfect qualitative agreement with single crystals. Starting from these films, we have also successfully fabricated nanowires with widths down to 65 nm, at different oxygen doping. The nanostructures exhibit characteristic temperatures (as the critical temperature Tc and the pseudogap temperature T∗) similar to those of the as-grown films and carry critical current densities Jc close to the critical depairing value, limited by vortex entry. This implies that the superconducting and the normal state properties of underdoped YBCO are preserved in our films, and they can be studied as a function of the dimensionality of the system, down to the nanoscale.
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| 6. |
- Arpaia, Riccardo, 1985, et al.
(author)
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Untwinned YBa2Cu3O7-delta thin films on MgO substrates: A platform to study strain effects on the local orders in cuprates
- 2019
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In: Physical Review Materials. - 2475-9953. ; 3:11
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Journal article (peer-reviewed)abstract
- We have grown untwinned YBa2Cu3O7-delta (YBCO) films on (110) MgO substrates that were preannealed at high temperature in oxygen atmosphere. The annealing results in surface reconstruction with shallow facets, which induce the suppression of the YBCO twinning domains, and the preferential alignment of the CuO chains along one of the in-plane directions of the substrate. Because of the large mismatch between the in-plane lattice parameters of film and substrate, the strain induced by the MgO into the YBCO layer is strong and very peculiar. The YBCO film is compressed, with respect to the bulk, and presents a unidirectional buckling of the atomic planes, along the chains' direction, due to a deformation of the copper-oxygen octahedra. The YBCO films, which can be grown with thicknesses down to few unit cells and oxygen doping levels spanning most of the superconducting dome, are patterned into nanowires with dimensions down to 50 nm. The anisotropies due to the untwinning state are preserved in these structures; moreover, additional anisotropies appear in ultrathin structures where strain effects become more pronounced. Such untwinned and compressively strained films can therefore be used as a platform to study the interplay between strain and the various local orders in the normal state of YBCO.
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| 7. |
- Baghdadi, Reza, 1984, et al.
(author)
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Study of in-plane electrical transport anisotropy of alpha-axis oriented YBa2Cu3O7-delta nanodevices
- 2017
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In: Physical Review B. - 2469-9969 .- 2469-9950. ; 95:18, s. Article no. 184505-
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Journal article (peer-reviewed)abstract
- In the present work, we report the growth of fully untwinned high-quality a-axis-oriented YBa2Cu3O7-delta films on (100) SrLaGaO4 substrates by using PrBa2Cu3O7-delta as a buffer layer. We also fabricated nanowires at different angles gamma with respect to the [0,1,0] direction of the substrate and studied the in-plane anisotropy of the critical current density, which we explained by considering the anisotropy in the coherence length xi and London penetration depth lambda L. Finally, half-integer Shapiro-like steps measured in slightly underdoped c-axis oriented (gamma = 90 degrees) nanowires point towards a different transport regime, which could shed light on intriguing issues of high-critical-temperature superconductors.
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| 8. |
- Kaiser, M., et al.
(author)
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VEDLIoT: Very Efficient Deep Learning in IoT
- 2022
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In: Proceedings of the 2022 Design, Automation and Test in Europe Conference and Exhibition, DATE 2022. - : IEEE. - 9783981926361
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Conference paper (peer-reviewed)abstract
- The VEDLIoT project targets the development of energy-efficient Deep Learning for distributed AIoT applications. A holistic approach is used to optimize algorithms while also dealing with safety and security challenges. The approach is based on a modular and scalable cognitive IoT hardware platform. Using modular microserver technology enables the user to configure the hardware to satisfy a wide range of applications. VEDLIoT offers a complete design flow for Next-Generation IoT devices required for collaboratively solving complex Deep Learning applications across distributed systems. The methods are tested on various use-cases ranging from Smart Home to Automotive and Industrial IoT appliances. VEDLIoT is an H2020 EU project which started in November 2020. It is currently in an intermediate stage with the first results available.
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| 9. |
- Trabaldo, Edoardo, 1990, et al.
(author)
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Grooved Dayem Nanobridges as Building Blocks of High-Performance YBa2Cu3O7−δ SQUID Magnetometers
- 2019
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 19:3, s. 1902-1907
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Journal article (peer-reviewed)abstract
- We present noise measurements performed on a YBa 2 Cu 3 O 7-δ nanoscale weak-link-based magnetometer consisting of a superconducting quantum interference device (SQUID) galvanically coupled to a 3.5 × 3.5 mm 2 pick-up loop, reaching white flux noise levels and magnetic noise levels as low as 6μÎ0/Hz and 100 fT/Hz at T = 77 K, respectively. The low noise is achieved by introducing grooved Dayem bridges (GDBs), a new concept of a weak link. A fabrication technique has been developed for the realization of nanoscale grooved bridges, which substitutes standard Dayem bridge weak links. The introduction of these novel key blocks reduces the parasitic inductance of the weak links and increases the differential resistance of the SQUIDs. This greatly improves the device performance, thus resulting in a reduction of the white noise.
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| 10. |
- Trabaldo, Edoardo, 1990, et al.
(author)
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Noise Properties of YBCO Nanostructures
- 2017
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In: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 27:4
-
Journal article (peer-reviewed)abstract
- Voltage noise measurements on close to optimally doped YBa2Cu3O7-delta nanostructures have been performed. The measured resistance noise at temperature T = 96 K (above critical temperature T-C = 85 K) shows a quadratic dependence on the bias current, e.g., the voltage power spectral density S-V alpha V-2. Moreover, the normalized voltage noise S-V/V-2 is inversely proportional to the device volume. This is a clear indication that the noise is the result of an ensemble of independent resistive fluctuators, evenly distributed within the sample volume. For our structures, we obtain a product S-V/V-2 x Vol. = const. approximate to 6 x 10-(33) m(3)/Hz resulting in a Hooge's parameter 3.4 x 10(-4), which is among the lowest reported in literature. At lower temperature, T = 2 K (well below TC) the total voltage fluctuations are given by the combined effect of critical current fluctuations and resistance fluctuations. For the critical current noise, we obtain a product S-I/IC2 x Vol. = const. approximate to 6x10(-32) m(3)/Hz. The larger value of the relative critical current noise is most probably due to the fact that the critical current is determined by edge effects whereas the resistance is given by the total volume of the device.
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