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Campi G.,CNR Institute of Neuroscience | Ricci A.,German Electron Synchrotron | Poccia N.,MESA Institute for Nanotechnology | Barba L.,Elettra - Sincrotrone Trieste | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Oxygen chain fragments are known to appear at the insulator-to- superconductor transition in YBa2Cu3O6+y. However, the self-organization and the size distribution of oxygen chain fragments are not known. Here, we seek to fill this gap, using scanning micro-x-ray diffraction, which is an imaging method based on advances in focusing a synchrotron radiation beam. This approach allows us to probe both real-space and k-space of high-quality YBa2Cu3O 6.33 single crystals with Tc = 7 K. We report compelling evidence for nanoscale striped puddles, with Ortho-II structure, made of chain fragments in the basal Cu(1) plane with local oxygen concentration y ≥ 0.5. The size of the Ortho-II puddles spans a range between 2 and 9 nm. The real-space imaging of Ortho-II puddles granular network shows that superconductivity, at a low hole-doping regime, occurs in a network of nanoscale oxygen ordered patches, interspersed with oxygen depleted regions. The manipulation by thermal treatments of the striped Ortho-II puddles has been investigated focusing on the spontaneous symmetry breaking near the order-to-disorder phase transition at T0 = 350 K. © 2013 American Physical Society.

Ricci A.,German Electron Synchrotron | Ricci A.,Rome International Center for Materials Science Superstripes | Poccia N.,Rome International Center for Materials Science Superstripes | Poccia N.,University of Twente | And 7 more authors.
Scientific Reports | Year: 2013

Despite intensive research a physical explanation of high Tc superconductors remains elusive. One reason for this is that these materials have generally a very complex structure making useless theoretical models for a homogeneous system. Little is known on the control of the critical temperature by the space disposition of defects because of lack of suitable experimental probes. X-ray diffraction and neutron scattering experiments used to investigate y oxygen dopants in YBa2 Cu3 O6+y lack of spatial resolution. Here we report the spatial imaging of dopants distribution inhomogeneity in YBa2 Cu3 O6.67 using scanning nano X-ray diffraction. By changing the X-ray beam size from 1 micron to 300 nm of diameter, the lattice inhomogeneity increases. The ordered oxygen puddles size distribution vary between 6-8 nm using 1 × 1μm2 beam, while it is between 5-12 nm with a fat tail using the 300 × 300 nm 2 beam. The increased inhomogeneity at the nanoscale points toward a network of superconducting puddles made of ordered oxygen interstitials.

Marcelli A.,National Institute of Nuclear Physics, Italy | Marcelli A.,Rome International Center for Materials Science Superstripes
Acta Physica Polonica A | Year: 2016

The X-ray absorption near edge structure spectroscopy is a unique powerful local and fast experimental method to study complex systems since it probes the nanoscale structure around selected atoms giving evidence for different local and instantaneous phases present in multiscale highly correlated granular systems. Transition metals and rare earth oxides like manganites, cuprates or pnictides superconductors show a rich variety of different competing structural, electronic and magnetic phases, which spatially coexist forming complex lattice textures. Many recent experimental data have pointed out the presence of arrested phase separation and the interplay of different phases occurring from nano- to micrometer-scale. This scenario opens the possibility to manipulate the mesoscopic phases to get new material functionalities. Therefore there is increasing need to develop methods to probe morphology and phase distribution at multiple length scales. Actually, combining X-ray imaging at high spatial resolution with μ-XANES spectroscopy both mesoscale, nanoscale and atomic structural changes can be identified. The μ-XANES spectroscopy technique is rapidly growing to investigate adaptive matter, high temperature superconductors, complex materials showing arrested phase separation at the mesoscale.

Bianconi A.,Rome International Center for Materials Science Superstripes | Bianconi A.,CNR Institute of Neuroscience | Bianconi A.,Consortium for Science and Technology of Materials | Jarlborg T.,Rome International Center for Materials Science Superstripes | Jarlborg T.,University of Geneva
EPL | Year: 2015

A recent experiment has shown a macroscopic quantum coherent condensate at 203 K, about 19 degrees above the coldest temperature recorded on the Earth surface, 184K (-89.2 °C,-128.6 °F) in pressurized sulfur hydride. This discovery is relevant not only in material science and condensed matter but also in other fields ranging from quantum computing to quantum physics of living matter. It has given the start to a gold rush looking for other macroscopic quantum coherent condensates in hydrides at the temperature range of living matter 200 < Tc < 400 K. We present here a review of the experimental results and the theoretical works and we discuss the Fermiology of H3S focusing on Lifshitz transitions as a function of pressure. We discuss the possible role of the shape resonance near a neck disrupting Lifshitz transition, in the Bianconi-Perali-Valletta (BPV) theory, for rising the critical temperature in a multigap superconductor, as the Feshbach resonance rises the critical temperature in Fermionic ultracold gases. © 2015 EPLA.

Jarlborg T.,University of Geneva | Bianconi A.,Rome International Center for Materials Science Superstripes | Bianconi A.,National Research Council Italy | Bianconi A.,University of Rome La Sapienza
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Novel imaging methods show that the mobile dopants in optimum doped La 2CuO4+y (LCO) get self-organized, instead of randomly distributed, to form an inhomogeneous network of nanoscale metallic puddles with ordered oxygen interstitials interspersed with oxygen-depleted regions. These puddles are expected to be metallic, being far from half filling because of high dopant density, and to sustain superconductivity having a size in the range 5-20 nm. However, the electronic structure of these heavily doped metallic puddles is not known. In fact the rigid-band model fails because of ordering of dopants and supercell calculations are required to obtain the Fermi surface reconstruction. We have performed advanced band calculations for a large supercell La16Cu8O32+N where N=1 or 2 oxygen interstitials form rows in the spacer La16O16+N layers intercalated between the CuO2 layers as determined by scanning nano x-ray diffraction. The additional occupied states made by interstitial oxygen orbitals sit well below the Fermi level (EF) and lead to hole doping as expected. The unexpected results show that in the heavily doped puddles the altered Cu(3d)-O(2p) band hybridization at EF induces a multiband electronic structure with the formation of multiple Fermi surface spots: (a) Small gaps appear in the folded Fermi surface, (b) three minibands cross E F with reduced Fermi energies of 60, 150, and 240 meV, respectively, (c) the density of states and band mass at EF show substantial increases, and (d) spin-polarized calculations show a moderate increase of antiferromagnetic spin fluctuations. All calculated features are favorable to enhance superconductivity; however, the comparison with experimental methods probing the average electronic structure of cuprates will require the description of the electronics of a network of multigap superconducting puddles. © 2013 American Physical Society.

Innocenti D.,Rome International Center for Materials Science Superstripes | Bianconi A.,Rome International Center for Materials Science Superstripes
Journal of Superconductivity and Novel Magnetism | Year: 2013

The doping dependent isotope effect in cuprates is explained in the framework of shape resonances in the superconducting gaps (belonging to the class of Fano resonances) in multicondensate superconductors. This new paradigm for high temperature superconductivity is based on the recent Fermiology scenario emerging from dHvA and quantum oscillation data showing a 2.5 Lifshitz topological transition due to the appearance of new small Fermi surface in the underdoped regime. The isotope effect is calculated for an electronic system near a band edge for a superlattice of stripes. The model reproduces the doping dependence of the isotope exponent behavior in cuprates and allows to identify the relative role of the intraband Cooper pairing and the configuration interaction between pairing channels from experimental data. © 2013 Springer Science+Business Media New York.

Bianconi A.,Rome International Center for Materials Science Superstripes
Journal of Superconductivity and Novel Magnetism | Year: 2014

Lattice and electronic nanoscale phase separation in strongly correlated multiband systems confined in heterostructure at atomic limit called superstripes has been an object of the scientific debate at the international conference Superstripes 2013 focusing on "Quantum in Complex Matter: Superconductivity, Magnetism and Ferroelectricity" held in Ischia, Italy (May 27-June 1, 2013). The focus was on lattice granularity due to defects self-organization, lattice modulations at a critical misfit strain, and electronic phase separation in multiband Hubbard models near a 2.5 Lifshitz transition. The emerging superstripes scenario is a particular case of percolation superconductivity in networks of superconducting multicondensates superconducting puddles and their competition with phase-separated networks of nanoscale-striped magnetic puddles. This new emerging paradigm for high-Tc superconductor-layered oxides opens new perspectives for quantum electronics by controlling the complexity in functional oxides. © 2014 Springer Science+Business Media New York.

Campi G.,CNR Institute of Neuroscience | Ciasca G.,Catholic University | Poccia N.,University of Twente | Ricci A.,German Electron Synchrotron | And 2 more authors.
Current Protein and Peptide Science | Year: 2014

The electrons transfer (ET) from an atom or a molecule, donor (D), to another, acceptor (A) is the basis of many fundamental chemical and physical processes. The ET mechanism is controlled by spatial arrangements of donor and acceptors: it's the particular spatial arrangement and thus the particular distance and the orientation between the electron donors and acceptors that controls the efficiency in charge separation processes in nature. Here, we stress the importance of this concept reviewing how spatial distribution of atomic and molecular self-assembly can determine the quality and physical features of ET process from biology to material science. In this context, we propose novel lab-on-chip techniques to be used to control spatial distribution of molecules at nanoscale. Synchrotron source brightness jointly to focusing optics fabrication allows one nowadays to monitor and visualize structures with sub-micrometric spatial resolution. This can give us a new powerful tool to set up sophisticated X-ray imaging techniques as well as spectroscopic elemental and chemical mapping to investigate the structure-function relationship controlling the spatial arrangement of the molecules at nanoscale. Finally, we report intriguing recent case studies on the possibility to manipulate and control this spatial distribution and material functionality at nanoscale by using X ray illumination. © 2014 Bentham Science Publishers.

Perali A.,University of Camerino | Perali A.,Mediterranean Institute of Fundamental Physics | Innocenti D.,University of Rome Tor Vergata | Valletta A.,CNR Institute for Microelectronics and Microsystems | And 2 more authors.
Superconductor Science and Technology | Year: 2012

The doping dependent isotope effect on the critical temperature (T c) is calculated for multi-band multi-condensate superconductivity near a 2.5 Lifshitz transition. We consider a superlattice of quantum stripes with finite hopping between stripes near a 2.5 Lifshitz transition for the appearance of a new sub-band making a circular electron-like Fermi surface pocket. We describe a particular type of BEC (Bose-Einstein Condensate) to BCS (Bardeen-Cooper-Schrieffer condensate) crossover in multi-band/multi-condensate superconductivity at a metal-to-metal transition that is quite different from the standard BEC-BCS crossover at an insulator-to-metal transition. The results show that the isotope coefficient strongly deviates from the standard BCS value 0.5, when the chemical potential is tuned at the 2.5 Lifshitz transition for the metal-to-metal transition. The critical temperature Tc shows a minimum due to the Fano antiresonance in the superconducting gaps and the isotope coefficient diverges at the point where a BEC coexists with a BCS condensate. In contrast Tc reaches its maximum and the isotope coefficient vanishes at the crossover from a polaronic condensate to a BCS condensate in the newly appearing sub-band. © 2012 IOP Publishing Ltd.

Bianconi A.,Rome International Center for Materials Science Superstripes
Journal of Physics: Conference Series | Year: 2013

A characteristic feature of a superconductor made of multiple condensates is the possibility of the shape resonances in superconducting gaps. Shape resonances belong to class of Fano resonances in configuration interaction between open and closed scattering channels. The Shape resonances arise because of the exchange interaction, a Josephson-like term, for transfer of pairs between different condensates in different Fermi surface spots in the special cases where at least one Fermi surface is near a 2.5 Lifshitz topological transition. We show that tuning the shape resonances show first, the gap suppression (like a Fano anti-resonance) driven by configuration interaction between a BCS condensate and a BEC-like condensate, and second, the gap amplification (like a Fano resonance) driven by configuration interaction between BCS condensates in large and small Fermi surfaces. Shape resonances usually occur in granular nanoscale complex matter (called superstripes) because of the lattice instability near a 2.5 Lifshitz transition in presence of interactions. Using a new imaging method, scanning nano-X-ray diffraction, we have shown the generic formation in high temperature superconductors of a granular superconducting networks made of striped puddles formed by ordered oxygen interstitials or ordered local lattice distortions (like static short range charge density waves). In the superconducting puddles the chemical potential is tuned to a shape resonance in superconducting gaps and the maximum Tc occurs where the puddles form scale free superconducting networks. © Published under licence by IOP Publishing Ltd.

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