| 1. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Dynamical charge density fluctuations pervading the phase diagram of a Cu-based high-Tc superconductor
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 365:6456, s. 906-910
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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High-temperature superconducting nanowires for photon detection
- 2015
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 509, s. 16-21
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Tidskriftsartikel (refereegranskat)abstract
- The possible use of high-temperature superconductors (HTS) for realizing superconducting nanowire single-photon detectors is a challenging, but also promising, aim because of their ultrafast electron relaxation times and high operating temperatures. The state-of-the-art HTS nanowires with a 50-nm thickness and widths down to 130 nm have been fabricated and tested under a 1550-nm wavelength laser irradiation. Experimental results presenting both the amplitude and rise times of the photoresponse signals as a function of the normalized detector bias current, measured in a wide temperature range, are discussed. The presence of two distinct regimes in the photoresponse temperature dependence is clearly evidenced, indicating that there are two different response mechanisms responsible for the HTS photoresponse mechanisms.
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| 3. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Improved noise performance of ultrathin YBCO Dayem bridge nanoSQUIDs
- 2017
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 30:1
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated YBa2Cu3O7-delta (YBCO) nano superconducting quantum interference devices (nanoSQUIDs), realized in Dayem bridge configuration, on films with thickness down to 10 nm. The devices, which have not been protected by a Au capping layer during the nanopatterning, show modulations of the critical current as a function of the externally applied magnetic field from 300 mK up to the critical temperature of the nanobridges. The absence of the Au shunting layer and the enhancement of the sheet resistance in ultrathin films lead to very large voltage modulations and transfer functions, which make these nanoSQUIDs highly sensitive devices. Indeed, by using bare YBCO nanostructures, we have revealed an upper limit for the intrinsic white flux noise level S-Phi,w(1/2)
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| 4. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Probing the phase diagram of cuprates with YBa2Cu3O7−δ thin films and nanowires
- 2018
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Ingår i: Physical Review Materials. - 2475-9953. ; 2:2
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Transport properties of ultrathin YBa2Cu3O7-delta nanowires: A route to single-photon detection
- 2017
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 96:6
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Tidskriftsartikel (refereegranskat)abstract
- We report on the growth and characterization of ultrathin YBa2Cu3O7-delta (YBCO) films on MgO (110) substrates, which exhibit superconducting properties at thicknesses down to 3 nm. YBCO nanowires, with thicknesses down to 10 nm and widths down to 65 nm, have also been successfully fabricated. The nanowires protected by a Au capping layer showsuperconducting properties close to the as-grown films and critical current densities, which are limited by only vortex dynamics. The 10-nm-thick YBCO nanowires without the Au capping present hysteretic current-voltage characteristics, characterized by a voltage switch which drives the nanowires directly from the superconducting to the normal state. We associate such bistability to the presence of localized normal domains within the superconductor. The presence of the voltage switch in ultrathin YBCO nanostructures, characterized by high sheet resistance values and high critical current values, makes our nanowires very attractive devices to engineer single-photon detectors.
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| 6. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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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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Ingår i: Physical Review Materials. - 2475-9953. ; 3:11
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Tidskriftsartikel (refereegranskat)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. |
- Arpaia, Riccardo, 1985
(författare)
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YBCO nanowires to study nanoscale ordering in High-Tc Superconductors
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We present the realization of YBa2Cu3O7-δ (YBCO) nanowires for both basic physics studies, which could help to elucidate the microscopic mechanisms of High critical Temperature Superconductors (HTS), and for novel applications.The first part of the thesis describes an improved nanopatterning procedure, based on e-beam lithography in combination with an amorphous carbon mask and a very gentle Ar+ ion etching. By using this procedure, nanowires preserving pristine superconducting properties, characterized by critical current densities very close to the theoretical depairing limit, have been achieved. These structures represent model systems for the study of HTS: their superconducting properties are very close to the as grown films. We have grown YBCO thin films covering a broad oxygen doping range going from the slightly overdoped regime down to the strongly underdoped region of the phase diagram. We have been able to trace the entire underdoped part of the phase diagram, and to show that the most peculiar features encountered in single crystals are well reproduced in our thin films.The core of the thesis describes an experiment done to study the effect of the nanoscale ordering on the superconducting properties of our nanowires. The presence of a local charge density wave (CDW) order has been recently demonstrated to be ubiquitous among all the cuprate families; if associated to a local modulations of Cooper pair density, CDWs might affect the absolute value of the critical current density of nanowires patterned at different in plane angles. We have used YBCO nanowires, fabricated on untwinned films, as a function of the oxygen doping and with dimensions of the same order as the CDW correlation length. By measuring the current voltage characteristic (IVC) of nanowires with the same width, patterned at different angles with respect to a fixed in plane direction of the substrate, we have revealed a cosinusoidal modulation of the critical current density for the narrowest width w (of the order of 65 nm). This dependence, that smears out for wider nanowire dimensions, can represent one of the first evidence of the existence of a pair density wave in YBCO.In the second part of the thesis we have focused on applications. YBCO nanoSQUIDs, employing very short nanowires in the so-called Dayem bridge configuration, have been fabricated and characterized. These devices, working in the whole temperature range from 300 mK up to the critical temperature TC (close to 85 K), have revealed an ultra low-white noise, below 1 µΦ0Hz-1/2 above 10 kHz, corresponding to a predicted spin sensitivity of 50 µBHz-1/2.The homogeneity of the nanowires has also given a boost to the realization of devices, aimed at the detection of single photons. We have shown that in ultrathin (7-8 unit cell thick) YBCO nanowires a hot spot is formed within the wire: as a consequence, the nanowires are driven from the superconducting directly to the normal state, analogously to NbN nanowires commonly used as single photon detectors.
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| 8. |
- Arzeo, Marco, 1986, et al.
(författare)
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Toward ultra high magnetic field sensitivity YBa2Cu3O7 - δ nanowire based superconducting quantum interference devices
- 2016
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 119:17
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Tidskriftsartikel (refereegranskat)abstract
- We report on measurements of YBa2Cu3O7- ? nanowire based Superconducting QUantum Interference Devices (nanoSQUIDs) directly coupled to an in-plane pick-up loop. The pick-up loop, which is coupled predominantly via kinetic inductance to the SQUID loop, allows for a significant increase of the effective area of our devices. Its role is systematically investigated and the increase in the effective area is successfully compared with numerical simulations. Large effective areas, together with the ultra low white flux noise below 1 ? ? 0 / Hz, make our nanoSQUIDs very attractive as magnetic field sensors.
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| 9. |
- Baghdadi, Reza, 1984, et al.
(författare)
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Fabricating Nanogaps in YBa2Cu3O7-delta for Hybrid Proximity-Based Josephson Junctions
- 2015
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Ingår i: Physical Review Applied. - 2331-7019. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- The advances of nanotechnologies applied to high-critical-temperature superconductors (HTSs) have recently given a huge boost to the field, opening new prospectives for their integration in hybrid devices. The feasibility of this research goes through the realization of HTS nanogaps with superconductive properties close to the as-grown bulk material at the nanoscale. Here we present a fabrication approach allowing the realization of YBa2Cu3O7-delta (YBCO) nanogaps with dimensions as small as 35 nm. To assess the quality of the nanogaps, we measure, before and after an ozone treatment, the current-voltage characteristics and the resistance versus temperature of YBCO nanowires with various widths and lengths, fabricated by using different lithographic processes. The analysis of the superconducting transition with a thermally activated vortex-entry model allows us to determine the maximum damage the nanowires undergo during the patterning which relates to the upper bound for the dimension of the nanogap. We find that the effective width of the nanogap is of the order of 100 nm at the superconducting transition temperature while retaining the geometrical value of about 35 nm at lower temperatures. The feasibility of the nanogaps for hybrid Josephson devices is demonstrated by bridging them with thin Au films. We detect a Josephson coupling up to 85 K with an almost ideal magnetic-field response of the Josephson current. These results pave the way for the realization of complex hybrid devices, where tiny HTS nanogaps can be instrumental to study the Josephson effect through barriers such as topological insulators or graphene.
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| 10. |
- Baghdadi, Reza, 1984, et al.
(författare)
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Study of in-plane electrical transport anisotropy of alpha-axis oriented YBa2Cu3O7-delta nanodevices
- 2017
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 95:18, s. Article no. 184505-
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Tidskriftsartikel (refereegranskat)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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