| 1. |
- Andersson, Eric, 1992, et al.
(författare)
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Fabrication and electrical transport characterization of high quality underdoped YBa2Cu3O7-δ nanowires
- 2020
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 33:6
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Tidskriftsartikel (refereegranskat)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. |
- 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
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 7:38, s. 15935-15944
-
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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| 3. |
- 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
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 365:6456, s. 906-910
-
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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| 4. |
- Arpaia, Riccardo, 1985, et al.
(författare)
-
Engineering underdoped CuO2 nanoribbons in nm-thick a -axis YBa2Cu3 O7-δ films
- 2024
-
Ingår i: Physical Review Materials. - 2475-9953. ; 8:4
-
Tidskriftsartikel (refereegranskat)abstract
- In underdoped cuprate high-Tc superconductors, various local orders and symmetry-breaking states, in addition to superconductivity, reside in the CuO2 planes. The confinement of the CuO2 planes can therefore play a fundamental role in modifying the hierarchy between the various orders and their intertwining with superconductivity. Here we present the growth of a-axis oriented YBa2Cu3O7-δ films, spanning the whole underdoped side of the phase diagram. In these samples, the CuO2 planes are confined by the film thickness, effectively forming unit-cell-thick nanoribbons. The unidirectional confinement at the nanoscale enhances the in-plane anisotropy of the films. By x-ray diffraction and resistance vs temperature measurements, we have discovered the suppression of the orthorhombic-to-tetragonal transition at low dopings, and a very high anisotropy of the normal state resistance in the b-c plane, the latter being connected to a weak coupling between adjacent CuO2 nanoribbons. These findings show that the samples we have grown represent a novel system, different from the bulk, where future experiments can possibly shed light on the rich and mysterious physics occurring within the CuO2 planes.
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| 5. |
- Arpaia, Riccardo, 1985, et al.
(författare)
-
Engineering underdoped CuO2 nanoribbons in nm-thick a -axis YBa2Cu3 O7-δ films
- 2024
-
Ingår i: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 8:4
-
Tidskriftsartikel (refereegranskat)abstract
- In underdoped cuprate high-Tc superconductors, various local orders and symmetry-breaking states, in addition to superconductivity, reside in the CuO2 planes. The confinement of the CuO2 planes can therefore play a fundamental role in modifying the hierarchy between the various orders and their intertwining with superconductivity. Here we present the growth of a-axis oriented YBa2Cu3O7-δ films, spanning the whole underdoped side of the phase diagram. In these samples, the CuO2 planes are confined by the film thickness, effectively forming unit-cell-thick nanoribbons. The unidirectional confinement at the nanoscale enhances the in-plane anisotropy of the films. By x-ray diffraction and resistance vs temperature measurements, we have discovered the suppression of the orthorhombic-to-tetragonal transition at low dopings, and a very high anisotropy of the normal state resistance in the b-c plane, the latter being connected to a weak coupling between adjacent CuO2 nanoribbons. These findings show that the samples we have grown represent a novel system, different from the bulk, where future experiments can possibly shed light on the rich and mysterious physics occurring within the CuO2 planes.
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| 6. |
- Arpaia, Riccardo, 1985, et al.
(författare)
-
High-temperature superconducting nanowires for photon detection
- 2015
-
Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 509, s. 16-21
-
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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| 7. |
- Arpaia, Riccardo, 1985, et al.
(författare)
-
Highly homogeneous YBCO/LSMO nanowires for photoresponse experiments
- 2014
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 27:4
-
Tidskriftsartikel (refereegranskat)abstract
- By using nanolithography and a soft etching procedure, we have realized YBa2Cu3O7-x/La0.7Sr0.3MnO3 (YBCO/LSMO) nanowires, with cross sections down to 100 x 50 nm(2) that ensure the cover age of areas up to 10 x 30 mu m(2). The LSMO layer acts as a capping for YBCO, minimizing the degradation of the superconducting properties taking place during the patterning; moreover, as a ferromagnetic manganite, it is expected to accelerate the relaxation dynamics of quasiparticles in YBCO, making such a system potentially attractive for applications in superconducting ultrafast optoelectronics. The reproducibility of the values of the critical current densities measured in different devices with the same geometry makes our nanowires ideal candidates for photoresponse experiments. First measurements have shown a satisfactory photoresponse from YBCO/LSMO devices.
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| 8. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Improved Nanopatterning for YBCO Nanowires Approaching the Depairing Current
- 2013
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 23:3
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Tidskriftsartikel (refereegranskat)abstract
- An improved nanopatterning procedure has been developed to obtain YBa2Cu3O7-x nanowires with cross-sections as small as 50 x 50 nm(2), protected by an Au capping layer. To probe the effective role of the Au protecting layer, we have measured the current-voltage characteristics and the resistive transition in temperature of the nanowires. Critical current densities up to 108 A/cm(2) have been achieved at T = 4.2 K, approaching the theoretical depairing current limit. The resistance, measured as a function of temperature close to T-c, has been fitted with a thermal activated phase slip model, including the effect of the gold layer. The extracted values of the superconducting coherence length and of the London penetration depth give current densities consistent with the measured ones. These results cannot be achieved with nanowires without the Au capping layer.
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| 9. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Improved noise performance of ultrathin YBCO Dayem bridge nanoSQUIDs
- 2017
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 30:1
-
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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| 10. |
- Arpaia, Riccardo, 1985, et al.
(författare)
-
Probing the phase diagram of cuprates with YBa2Cu3O7−δ thin films and nanowires
- 2018
-
Ingår i: Physical Review Materials. - 2475-9953. ; 2:2
-
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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| 11. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Resistive state triggered by vortex entry in YBa2Cu3O7-delta nanostructures
- 2014
-
Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 506, s. 165-168
-
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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| 12. |
- Arpaia, Riccardo, 1985, et al.
(författare)
-
Signature of quantum criticality in cuprates by charge density fluctuations
- 2023
-
Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 14:1
-
Tidskriftsartikel (refereegranskat)abstract
- The universality of the strange metal phase in many quantum materials is often attributed to the presence of a quantum critical point (QCP), a zero-temperature phase transition ruled by quantum fluctuations. In cuprates, where superconductivity hinders direct QCP observation, indirect evidence comes from the identification of fluctuations compatible with the strange metal phase. Here we show that the recently discovered charge density fluctuations (CDF) possess the right properties to be associated to a quantum phase transition. Using resonant x-ray scattering, we studied the CDF in two families of cuprate superconductors across a wide doping range (up to p = 0.22). At p* ≈ 0.19, the putative QCP, the CDF intensity peaks, and the characteristic energy Δ is minimum, marking a wedge-shaped region in the phase diagram indicative of a quantum critical behavior, albeit with anomalies. These findings strengthen the role of charge order in explaining strange metal phenomenology and provide insights into high-temperature superconductivity.
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| 13. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Transport properties of ultrathin YBa2Cu3O7-delta nanowires: A route to single-photon detection
- 2017
-
Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 96:6
-
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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| 14. |
- Arpaia, Riccardo, 1985, et al.
(författare)
-
Ultra low noise YBa2Cu3O7-delta nano superconducting quantum interference devices implementing nanowires
- 2014
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:7
-
Tidskriftsartikel (refereegranskat)abstract
- We present results on ultra low noise YBa2Cu3O7-delta (YBCO) nano Superconducting QUantum Interference Devices (nanoSQUIDs). To realize such devices, we implemented high quality YBCO nanowires, working as weak links between two electrodes. We observe critical current modulation as a function of an externally applied magnetic field in the full temperature range below the transition temperature T-C. The white flux noise below 1 mu Phi(0)/root Hz at T = 8K makes our nanoSQUIDs very attractive for the detection of small spin systems.
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| 15. |
- Arpaia, Riccardo, 1985, et al.
(författare)
-
Untwinned YBa2Cu3O7-delta thin films on MgO substrates: A platform to study strain effects on the local orders in cuprates
- 2019
-
Ingår i: Physical Review Materials. - 2475-9953. ; 3:11
-
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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| 16. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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YBa2Cu3O7-delta nanorings to probe fluxoid quantization in High Critical Temperature Superconductors
- 2014
-
Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 506, s. 184-187
-
Tidskriftsartikel (refereegranskat)abstract
- We have realized YBa2Cu3O7-delta (YBCO) nanorings and measured the magnetoresistance R(B) close to the superconducting transition. The large oscillations that we have measured can be interpreted in terms of vortex dynamics triggering the nanowires to the resistive state. The Fast Fourier Transform spectrum of the magnetoresistance oscillations shows a single sharp peak for nanorings with narrower loop arm width: this peak can be univocally associated to a h/2e periodicity as predicted for optimally doped YBCO. Moreover it is a clear evidence of a uniform vorticity of the order parameter inside the rings, confirming a high degree of homogeneity of our nanostructures. This result gives a boost to further investigations of YBCO nanorings at different dopings within the superconducting dome, where in the underdoped regime a R(B) periodicity different from the conventional h/2e has been predicted.
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| 17. |
- Arzeo, Marco, 1986, et al.
(författare)
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Microwave losses in MgO, LaAlO3, and (La0.3Sr0.7)(Al0.65Ta0.35)O-3 dielectrics at low power and in the millikelvin temperature range
- 2014
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:21
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated both the temperature and the power dependence of microwave losses for various dielectrics commonly used as substrates for the growth of high critical temperature superconductor thin films. We present measurement of niobium superconducting lambda/2 coplanar waveguide resonators, fabricated on MgO, LaAlO3, and (La0.3Sr0.7)(Al0.65Ta0.35)O-3 (LSAT), at the millikelvin temperature range and at low input power. By comparing our results with the two-level system model, we have discriminated among different dominant loss mechanisms. LSAT has shown the best results as regards the dielectric losses in the investigated regimes.
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| 18. |
- Arzeo, Marco, 1986, et al.
(författare)
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Microwave losses in YBCO coplanar waveguide resonators at low power and millikelvin range
- 2015
-
Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 25:3
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the temperature dependence of microwave losses in the low-power limit and millikelvin temperature range of a thin-film YBa2Cu3O7-x (YBCO) λ/2 coplanar waveguide resonator patterned on a (La0.3Sr0.7) (Al0.65Ta0.35)O3 (LSAT) substrate covered by a CeO2 seed layer. The unloaded quality factor is mainly governed by the surface resistance of the YBCO film and the dielectric losses caused by resonant absorption due to a bath of two-level fluctuators in the dielectrics. The value of the unloaded quality factor at 20 mK and low power, i.e., Q0∼2000, allows for the realization of YBCO microwave quantum circuits implementing biepitaxial grain-boundary Josephson junctions.
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| 19. |
- 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
-
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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| 20. |
- Aurino, Pier Paolo, 1985, et al.
(författare)
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Retention of Electronic Conductivity in LaAlO3/SrTiO3 Nanostructures Using a SrCuO2 Capping Layer
- 2016
-
Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 6:2
-
Tidskriftsartikel (refereegranskat)abstract
- The interface between two wide band-gap insulators, LaAlO3 and SrTiO3 (LAO/STO) offers a unique playground to study the interplay and competitions between different ordering phenomena in a strongly correlated two- dimensional electron gas. Recent studies of the LAO/STO interface reveal the inhomogeneous nature of the 2DEG that strongly influences electrical-transport properties. Nanowires needed in future applications may be adversely affected, and our aim is, thus, to produce a more homogeneous electron gas. In this work, we demonstrate that nanostructures fabricated in the quasi-2DEG at the LaAlO3/SrTiO3 interface, capped with a SrCuO2 layer, retain their electrical resistivity and mobility independent of the structure size, ranging from 100 nm to 30 mu m. This is in contrast to noncapped LAO/STO structures, where the room-temperature electrical resistivity significantly increases when the structure size becomes smaller than 1 mu m. High-resolution intermodulation electrostatic force microscopy reveals an inhomogeneous surface potential with "puddles" of a characteristic size of 130 nm in the noncapped samples and a more uniform surface potential with a larger characteristic size of the puddles in the capped samples. In addition, capped structures show superconductivity below 200 mK and nonlinear currentvoltage characteristics with a clear critical current observed up to 700 mK. Our findings shed light on the complicated nature of the 2DEG at the LAO/STO interface and may also be used for the design of electronic devices.
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| 21. |
- Baghdadi, Reza, 1984, et al.
(författare)
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Fabricating Nanogaps in YBa2Cu3O7-delta for Hybrid Proximity-Based Josephson Junctions
- 2015
-
Ingår i: Physical Review Applied. - 2331-7019. ; 4:1
-
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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| 22. |
- Baghdadi, Reza, 1984, et al.
(författare)
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Josephson effect through YBa2Cu3 O7-δ /Au-encapsulated nanogaps
- 2017
-
Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 95:17
-
Tidskriftsartikel (refereegranskat)abstract
- We successfully fabricated and studied planar superconductor-normal-superconductor (SNS) Josephson junctions made of YBa2Cu3O7-? (YBCO) high-TC superconductor (S) and Au normal metal (N). The crucial step in fabrication was done by using a Pt/Au bilayer encapsulation of the patterned YBCO nanogap. This procedure preserves the YBCO nanogap from the degradation due to the contact with resists, water, and chemicals involved in further processing for hybrid devices. The junctions exhibit Fraunhofer-like modulation patterns and Shapiro steps when they are irradiated by a rf field. Furthermore, we analyzed the IC(T) characteristics of our hybrid junctions employing a SINI?S (superconductor-insulator-normal conductor-insulator-superconductor) model.
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| 23. |
- 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
-
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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| 24. |
- Baghdadi, Reza, 1984, et al.
(författare)
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Toward YBa2Cu3O7-δ nanoscale structures for hybrid devices
- 2015
-
Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 25:3
-
Tidskriftsartikel (refereegranskat)abstract
- An ex situ ozone annealing has been applied both on YBa2Cu3O7-d (YBCO) films and nanowires. From the investigation on bare films, by measuring the superconducting resistive transition in temperature and the X-ray diffraction pattern, we have observed that the ozonation can be a powerful tool to oxygenate the YBCO structure. To probe the effective role of this reactive annealing on nanostructures, we have fabricated nanowires with widths down to 100 nm, covered by a 20-nm-thick Au layer. We have compared the critical current density and the broadening of the resistance transition measured before and after the ozone treatment, concluding that the ozone is instrumental in recovering very high quality superconducting properties inside the nanostructures, which were degraded by the oxygen out-diffusion occurring during the nanopatterning.
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| 25. |
- Barone, A., et al.
(författare)
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Macroscopic quantum phenomena in Josephson structures
- 2010
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 36:10-11, s. 876-883
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Tidskriftsartikel (refereegranskat)abstract
- The Josephson effect is a probe with unparalleled capabilities for the study of a variety of macroscopic quantum phenomena. This is a survey of important achievements and challenging trends, in particular macroscopic quantum tunneling and energy level quantization. We focus on high-T-C superconducting structures and recent research on nanostructures.
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| 26. |
- Bauch, Thilo, 1972, et al.
(författare)
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Dynamics of d-wave YBa2Cu3O7-x
- 2007
-
Ingår i: Superconductor Science and Technology. - 0953-2048 .- 1361-6668. ; 20:2, s. S98-S104
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Konferensbidrag (refereegranskat)abstract
- The predominant d-wave pairing symmetry in high temperature superconductors leads to an unconventional current phase relation in Josephson junctions. This circumstance may induce new effects in the dynamics of dc SQUIDs. In this contribution we report on the measurements of the dependence of the SQUID Josephson current on the external magnetic field taken at very low temperatures, down to 20 mK. Different grain boundaries have been fabricated by using the biepitaxial and the bicrystal technique. Some of the effects which are induced by a nonsinusoidal current phase relation can be clearly identified in the dynamics of the SQUIDs. The experimental data are also compared with theoretical simulations taking into account the inductance of the loop. The data show that, in specific conditions, a non-negligible inductance of the loop can induce effects similar to an unconventional current phase relation, with a pronounced second harmonic sin(2) term. This fact has to be taken into account when designing d-wave SQUIDs for quantum circuitry.
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| 27. |
- Bauch, Thilo, 1972, et al.
(författare)
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High critical temperature superconductor Josephson junctions for quantum circuit applications
- 2009
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Ingår i: Physica Scripta. ; T137, s. 014006-
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Konferensbidrag (refereegranskat)abstract
- Recent findings of macroscopic quantum properties in high critical temperature superconductor (HTS) Josephson junctions (JJs) point toward the need to revise the role of zero energy quasi-particles in this novel superconductor. We will discuss the possibility of designing superconducting artificial atoms in a transmon configuration to study the low energy excitation spectra of HTS. We have engineered high quality grain boundary JJs on low dielectric constant substrates. By fabricating submicron junctions, we extract values of capacitance and Josephson critical current densities that satisfy the main transmon design requirements. Moreover, the measured critical current noise power extrapolated at 1 Hz gives a dephasing time of 25 ns, which indicates that the observation of macroscopic quantum coherent effects in HTS JJ is a feasible task.
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| 28. |
- Bauch, Thilo, 1972, et al.
(författare)
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High Frequency Properties of Josephson Junctions
- 2019
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Ingår i: Springer Series in Materials Science. - Cham : Springer International Publishing. - 2196-2812 .- 0933-033X. ; 286, s. 513-528
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this chapter we will discuss the high frequency properties of Josephson junctions. In the first part we review the effect of a large ac perturbation on the current voltage characteristic (IVC) of a Josephson junction. Here we follow closely the original treatment by Barone and Paterno [1]. For large ac perturbations the externally applied microwave frequency (and integer multiples of it) lock to the Josephson oscillation causing distinct current steps at fixed voltage values in the IVC. In the second part we give a short overview on the response of an underdamped Josephson junction to small microwave perturbations. In this case, when the applied microwave frequency is in resonance with the electromagnetic plasma frequency higher levels of this plasma mode get excited. This mechanism, also called resonant activation, leads for instance to a premature switching from the zero voltage state to the finite voltage state of a current biased Josephson junction. This procedure can be exploited to detect the quantized nature, i.e. the quantized energy levels, of the plasma modes. In fact the lowest two quantized energy levels of the plasma resonance mode are the key ingredient of superconducting qubits, such as the phase qubit and the transmon qubit.
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| 29. |
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| 30. |
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| 31. |
- Bauch, Thilo, 1972, et al.
(författare)
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YBCOSQUIDs with unconventional current phase relation
- 2007
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 463-465:1 October 2007, s. 979-984
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the dynamics of YBa2Cu3O7-delta,5 (YBCO) dc sperconducting quantum interference devices (SQUIDs) characterized by an unconventional Josephson current phase relation (CPR). We have focused on SQUID configurations with Josephson junctions where the lobe of the order parameter in one electrode is facing a node in the other electrode. This order parameter arrangement should enhance the appearance of a sin(2(p) term in the CPR. The response of the critical current of the dc SQUID, under the effect of an external magnetic field, has been measured in temperature, down to 20 mK. Our experimental data have been compared with numerical simulations of the SQUIDs dynamics by considering a CPR of a single junction of the form I(phi) = I-I sin(phi) - I-II sin(2 phi) where I-I, and I-II are, respectively, the first and second harmonic component. In our devices the values of the sin(2 phi) term are such that the fundamental state of the SQUID is naturally double degenerate. This is of great relevance for applications of d-wave SQUIDs in quantum information processing. (C) 2007 Elsevier B.V. All rights reserved.
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| 32. |
- Black-Schaffer, Annica M., et al.
(författare)
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Model Evidence of a Superconducting State with a Full Energy Gap in Small Cuprate Islands
- 2013
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 110:19, s. 197001-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate subdominant order parameters stabilizing at low temperatures in nanoscale high-Tc cuprate islands, motivated by the recent observation of a fully gapped state in nanosized YBa2Cu3O7-δ[D. Gustafsson et al., Nature Nanotech. 8, 25 (2013)]. Using complementary quasiclassical and tight-binding Bogoliubov–de Gennes methods, we show on distinctly different properties dependent on the symmetry being dx2-y2 þ is or dx2-y2 þ idxy. We find that a surface-induced dx2-y2 þ is phase creates a global spectroscopic gap which increases with an applied magnetic field, consistent with experimental observation.
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| 33. |
- Born, D., et al.
(författare)
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CaBaCuO ultrathin films and junctions
- 2007
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 17:2/3, s. 3581-3584
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Tidskriftsartikel (refereegranskat)abstract
- We investigated transport properties of ultrathin CaBaCuO (CBCO) bridges, focusing on vortex dynamics, and Josephson bicrystal junctions. The CBCO films used are composed of a stacking sequence of two structural subunits having different functions, namely a Ba-based charge reservoir (CR) block and a Ca-based infinite layer (IL) superconducting block. SQUID microscopy investigations of these films provide Pearl lengths A more than the bridge widths. Measuring current-voltage characteristics we found evidence that at high temperatures the vortices are thermally activated at the edge of the bridge and pushed in, causing dissipation and a power-law dependence of the voltage from the current. At lower temperatures, the experimental curves change their shape. We compared these data with the predicted behavior for vortex quantum tunneling and we found very good agreement. Moreover, we have realized Josephson junctions composed of only a few superconducting CuO2 planes. The CBCO films used in these experiments are only 8 nm thick and have six superconducting CUO2 planes. The simple structure of the GB allows a reliable estimation of the coupling along the ab planes of the CuO2. We calculate for 24 degrees symmetric and asymmetric cases a critical current density per plane of about (1-3) kA/cm(2).
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| 34. |
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| 35. |
- Calavalle, Francesco, et al.
(författare)
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Tailoring Superconductivity in Large-Area Single-Layer NbSe2 via Self-Assembled Molecular Adlayers
- 2021
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 21:1, s. 136-143
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional transition metal dichalcogenides (TMDs) represent an ideal testbench for the search of materials by design, because their optoelectronic properties can be manipulated through surface engineering and molecular functionalization. However, the impact of molecules on intrinsic physical properties of TMDs, such as superconductivity, remains largely unexplored. In this work, the critical temperature (TC) of large-area NbSe2 monolayers is manipulated, employing ultrathin molecular adlayers. Spectroscopic evidence indicates that aligned molecular dipoles within the self-assembled layers act as a fixed gate terminal, collectively generating a macroscopic electrostatic field on NbSe2. This results in an ∼55% increase and a 70% decrease in TC depending on the electric field polarity, which is controlled via molecular selection. The reported functionalization, which improves the air stability of NbSe2, is efficient, practical, up-scalable, and suited to functionalize large-area TMDs. Our results indicate the potential of hybrid 2D materials as a novel platform for tunable superconductivity.
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| 36. |
- Cedergren, Karin, 1975, et al.
(författare)
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Biepitaxial YBa2Cu3O7-x 0-pi Josephson junctions
- 2010
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 23:3, s. Article Number: 034027-
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements performed on YBa2Cu3O7-x '0' and '0-pi' Josephson junctions fabricated using the biepitaxial technique with SrTiO3 as substrate and CeO2 as seed layer. Measurements of the critical current as a function of external magnetic field clearly show complementary behavior of the two kinds of junctions. Our results unambiguously show that the d-wave nature of the order parameter dominates the current transport across the junctions despite the faceting on the microscale along the grain boundary line.
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| 37. |
- Cedergren, Karin, 1975, et al.
(författare)
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Interplay between Static and Dynamic Properties of Semifluxons in YBa2Cu3O7−δ 0−π Josephson Junctions
- 2010
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 104:17, s. 177003 -
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the static and dynamic properties of long YBa2Cu3O7-delta 0-pi Josephson junctions and compared them with those of conventional 0 junctions. Scanning SQUID microscope imaging has revealed the presence of a semifluxon at the phase discontinuity point in 0-pi Josephson junctions. Zero field steps have been detected in the current-voltage characteristics of all junctions. Comparison with simulation allows us to attribute these steps to fluxons traveling in the junction for conventional 0 junctions and to fluxon-semifluxon interactions in the case of 0-pi Josephson junctions.
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| 38. |
- Charpentier, Sophie, 1983, et al.
(författare)
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Hot spot formation in electron-doped PCCO nanobridges
- 2016
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 94:6
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the transport properties of optimally doped Pr2-xCexCuO4-δ (PCCO) nanobridges with width down to 100 nm. The critical current density of the nanobridges approaches the Ginzburg-Landau theoretical limit, which demonstrates nanostructures with properties close to the as-grown films. The current voltage characteristics are hysteretic with a sharp voltage switch, of the order of a few millivolts, that we interpret with the occurrence of a hot spot formation. The values of the retrapping current and the voltage switch obtained by modeling the heat transport in the nanobridges are very close to the experimental ones. This feature, together with the extremely short recombination times, make PCCO nanostructures attractive candidates for ultrafast single photon detectors.
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| 39. |
- 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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| 40. |
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| 41. |
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| 42. |
- Ejrnaes, M., et al.
(författare)
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Observation of dark pulses in 10nm thick YBCO nanostrips presenting hysteretic current voltage characteristics
- 2017
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 30:12
-
Tidskriftsartikel (refereegranskat)abstract
- We have fabricated several 10 nm thick and 65 nm wide YBa2Cu3O7-? (YBCO) nanostrips. The nanostrips with the highest critical current densities are characterized by hysteretic current voltage characteristics (IVCs) with a direct bistable switch from the zero-voltage to the finite voltage state. The presence of hysteretic IVCs allowed the observation of dark pulses due to fluctuations phenomena. The key role of the bistable behavior is its ability to transform a small disturbance (e.g. an intrinsic fluctuation) into a measurable transient signal, i.e. a dark pulse. On the contrary, in devices characterized by lower critical current density values, the IVCs are nonhysteretic and dark pulses have not been observed. To investigate the physical origin of the dark pulses, we have measured the bias current dependence of the dark pulse rate: The observed exponential increase with the bias current is compatible with mechanisms based on thermal activation of magnetic vortices in the nanostrip. We believe that the successful amplification of small fluctuation events into measurable signals in nanostrips of ultrathin YBCO is a milestone for further investigation of YBCO nanostrips for superconducting nanostrip single photon detectors and other quantum detectors for operation at higher temperatures.
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| 43. |
- 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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| 44. |
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| 45. |
- 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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| 46. |
- Galletti, L., et al.
(författare)
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Influence of topological edge states on the properties of Al/Bi2Se3/Al hybrid Josephson devices
- 2014
-
Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 89:13
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Tidskriftsartikel (refereegranskat)abstract
- In superconductor-topological insulator-superconductor hybrid junctions, the barrier edge states are expected to be protected against backscattering, to generate unconventional proximity effects, and, possibly, to signal the presence of Majorana fermions. The standards of proximity modes for these types of structures have to be settled for a neat identification of possible new entities. Through a systematic and complete set of measurements of the Josephson properties we find evidence of ballistic transport in coplanar Al-Bi2Se3-Al junctions that we attribute to a coherent transport through the topological edge state. The shunting effect of the bulk only influences the normal transport. This behavior, which can be considered to some extent universal, is fairly independent of the specific features of superconducting electrodes. A comparative study of Shubnikov-de Haas oscillations and scanning tunneling spectroscopy gave an experimental signature compatible with a two-dimensional electron transport channel with a Dirac dispersion relation. A reduction of the size of the Bi2Se3 flakes to the nanoscale is an unavoidable step to drive Josephson junctions in the proper regime to detect possible distinctive features of Majorana fermions.
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| 47. |
- Galletti, L., et al.
(författare)
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Josephson effect in Al/Bi2Se3/Al coplanar hybrid devices
- 2014
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 503, s. 162-165
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Tidskriftsartikel (refereegranskat)abstract
- The edge states of Topological Insulators (TI) are protected against backscattering, thanks to the topological properties arising from their band structure. Coupling a TI to a superconductor (S) can induce unconventional effects, including the creation of Majorana bound states (MBS). The fabrication of coplanar hybrid devices is a fundamental step to pave the way to the understanding of proximity effects in topologically non-trivial systems, and to a large variety of experiments aimed at the possible detection of MBS. We discuss the feasibility and some relevant properties of Al-Bi2Se3-Al coplanar proximity devices. Special attention is devoted to the design of the junction, aimed at enhancing the coupling between the electrodes and the TI.
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| 48. |
- Golubev, D., et al.
(författare)
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Effect of heating on critical current of YBCO nanowires
- 2014
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 506, s. 174-177
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Tidskriftsartikel (refereegranskat)abstract
- We discuss transport of heat in YBCO nanowires and its implications to their superconducting properties. We find under which conditions the central part of a nanowire may turn normal. We demonstrate that in long wires it may happen at currents much lower than the theoretical value of superconducting critical current. We derive a simple formula for the corresponding threshold current in terms of the heat transport parameters of YBCO. Our results may be interesting in view of potential applications of YBCO nanowires in detectors of radiation.
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| 49. |
- Golubev, Dmitry, et al.
(författare)
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Josephson Effect in Graphene and 3D Topological Insulators
- 2019
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Ingår i: Springer Series in Materials Science. - Cham : Springer International Publishing. - 2196-2812 .- 0933-033X. ; 286, s. 529-553
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The study of the proximity effect between a superconductor and a semiconductor or an unconventional metal, has lately received a dramatic boost due to the increasing possibilities to manufacture a larger variety of interfaces and materials.
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| 50. |
- Gustafsson, David, 1982, et al.
(författare)
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Fully gapped superconductivity in a nanometresize YBa2Cu3O7-delta island enhanced by a magnetic field
- 2013
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Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 8:1, s. 25-30
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Tidskriftsartikel (refereegranskat)abstract
- The symmetry of Cooper pairs is central to constructing a superconducting state. The demonstration of a d(x2-y2)-wave order parameter with nodes represented a breakthrough for high critical temperature superconductors (HTSs)(1,2). However, despite this fundamental discovery, the origin of superconductivity remains elusive, raising the question of whether something is missing from the global picture. Deviations from d(x2-y2)-wave symmetry(3,4), such as an imaginary admixture d(x2-y2) + is (or id(xy)), predict a ground state with unconventional properties exhibiting a full superconducting gap and time reversal symmetry breaking(5). The existence of such a state, until now highly controversial(6-10), can be proved by highly sensitive measurements of the excitation spectrum. Here, we present a spectroscopic technique based on an HTS nanoscale device that allows an unprecedented energy resolution thanks to Coulomb blockade effects, a regime practically inaccessible in these materials previously. We find that the energy required to add an extra electron depends on the parity (odd/even) of the excess electrons on the island and increases with magnetic field. This is inconsistent with a pure d(x2-y2)-wave symmetry and demonstrates a complex order parameter component that needs to be incorporated into any theoretical model of HTS.
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