arXiv subjects

Antonio Bianconi

Publications and source records attributed to Antonio Bianconi.

At least 37 records · Page 2Linked to original sources

arXiv2020

Ostwald growth rate in controlled Covid-19 epidemic spreading as in arrested growth in quantum complex matter

Here, we focus on the data analysis of the growth of epidemic spread of Covid-19 in countries where different policies of containment were activated. It is known that the growth of pandemic spread at its threshold is exponential, but it is not known how to quantify the success of different containment policies. We identify that a successful approach gives an arrested phase regime following the Ostwald growth, where, over the course of time, one phase transforms into another metastable phase with a similar free energy as observed in oxygen interstitial diffusion in quantum complex matter and in crystallization of proteins. We introduce the s factor which provides a quantitative measure of the efficiency and speed of the adopted containment policy, which is very helpful not only to monitor the Covid-19 pandemic spread but also for other countries to choose the best containment policy. The results show that a policy based on joint confinement, targeted tests, and tracking positive cases is the most rapid pandemic containment policy; in fact, we found values of 9, 5, and 31 for the success s factor for China, South Korea, and Italy, respectively, where the lowest s factor indicates the best containment policy

physics.soc-ph↗

arXiv2019

Ninety years of X-ray spectroscopy in Italy 1896-1986

Ninety years of X-ray spectroscopy research in Italy, from the X-rays discovery (1896), and the Fermi group theoretical research (1922-1938) to the Synchrotron Radiation research in Frascati from 1963 to 1986 are here summarized showing a coherent scientific evolution which has evolved into the actual multidisciplinary research on complex phases of condensed matter with synchrotron radiation.

cond-mat.mtrl-sci↗

arXiv2019

Multi-Band Superconductivity and the Steep Band -- Flat Band Scenario

The basic features of multi-band superconductivity and its implications are derived. In particular, it is shown that enhancements of the superconducting transition temperature take place due to interband interactions. In addition, isotope effects differ substantially from the typical BCS scheme as soon as polaronic coupling effects are present. Special cases of the model are polaronic coupling in one band as realized e.g., in cuprates, coexistence of a flat band and a steep band like in MgB2, crossovers between extreme cases. The advantages of the multiband approach as compared to the single band BCS model are elucidated and its rather frequent realization in actual systems discussed

cond-mat.supr-con↗

arXiv2019

Fermi-Bose mixtures and BCS-BEC crossover in high-Tc superconductors

In this review article we consider theoretically and give experimental support to the models of the Fermi-Bose mixtures and the BCS-BEC crossover compared with the strong-coupling approach, which can serve as the cornerstones on the way from high-temperature to room-temperature superconductivity in pressurized metallic hydrides. We discuss some key theoretical ideas and mechanisms proposed for unconventional superconductors (cuprates, pnictides, chalcogenides, bismuthates, diborides, heavy-fermions, organics, bilayer graphene, twisted graphene, oxide hetero-structures), superfluids and balanced or imbalanced ultracold Fermi gases in magnetic traps. We build a bridge between unconventional superconductors and recently discovered pressurized hydrides superconductors H3S and LaH10 with the critical temperature close to room temperature. We discuss systems with line of nodal Dirac points close to the Fermi surface, superconducting shape resonances and hyperbolic superconducting networks which are very important for the development of novel topological superconductors, for the energetics, for the applications in nano-electronics and quantum computations.

cond-mat.supr-con↗

arXiv2019

Direct Visualization of Spatial inhomogeneity of Spin Stripes Order in La1.72Sr0.28NiO4

In several strongly correlated electron systems, defects, charge and local lattice distortions are found to show complex inhomogeneous spatial distributions. There is growing evidence that such inhomogeneity plays a fundamental role in unique functionality of quantum complex materials. La1.72Sr0.28NiO4 is a prototypical strongly correlated material showing spin striped order associated with lattice and charge modulations. In this work we present the spatial distribution of the spin organization by applying micro X-ray diffraction to La1.72Sr0.28NiO4, mapping the spin-density-wave order below the 120K onset temperature. We find that the spin-density-wave order shows the formation of nanoscale puddles with large spatial fluctuations. The nano-puddle density changes on the microscopic scale forming a multiscale phase separation extending from nanoscale to micron scale with scale-free distribution. Indeed spin-density-wave striped puddles are disconnected by spatial regions with different stripe orientation or negligible spin-density-wave order. The present work highlights the complex nanoscale phase separation of spin stripes in nickelate perovskites and opens the question of the energetics at domain interfaces

cond-mat.mes-hall↗

arXiv2019

Evolution of Complexity in Out-of-Equilibrium Systems by Time-Resolved or Space-Resolved Synchrotron Radiation Techniques

Out-of-equilibrium phenomena are attracting high interest in physics, materials science, chemistry and life sciences. In this state, the study of structural fluctuations at different length scales in time and space are necessary to achieve significant advances in the understanding of structure-functionality relationship. The visualization of patterns arising from spatiotemporal fluctuations is nowadays possible thanks to new advances in X-ray instrumentation development that combine high resolution both in space and in time. We present novel experimental approaches using high brilliance synchrotron radiation sources, fast detectors and focusing optics, joint with advanced data analysis based on automated statistical, mathematical and imaging processing tools. This approach has been used to investigate structural fluctuations in out-of-equilibrium systems in the novel field of inhomogeneous quantum complex matter at the crossing point of technology, physics and biology. In particular, we discuss how nanoscale complexity controls the emergence of high temperature superconductivity (HTS), myelin functionality and formation of hybrid organic-inorganic nanostructures. The emergent complex geometries, opening novel venues to quantum technology and to development of quantum physics of living systems, are discussed

cond-mat.supr-con↗

arXiv2019

Is there any hidden symmetry in the stripe structure of perovskite high temperature superconductors?

Local and fast structural probes using synchrotron radiation have shown nanoscale striped puddles and nanoscale phase separation in doped perovskites.It is known that the striped phases in doped perovskites are due to competing interactions involving charge, spin and lattice degrees of freedom,but while many theoretical models for spin and charge stripes have been proposed we are missing theoretical models describing the complex lattice striped modulations in doped perovskites. In this work we show that two different stripes can be represented as a superposition of a pair of stripes, U(theta_n) and D(theta_n), characterized by perovskite tilts where one of the pair is rotated in relation to the other partner by an angle Delta(theta _n)=pi/2. The spatial distribution of the U and D stripes is reduced to all possible maps in the well-known mathematical four-color theorem. Both the periodic striped puddles and random structures can be represented by using $planar$ graphs with a chromatic number. To observe the colors in mapping experiments, it is necessary to recover variously oriented tilting effects from the replica. It is established that there is an interplay between the annihilation/creation of new stripes and ordering/disordering tilts in relation to the theta _n angle in the CuO2 plane, where the characteristic shape of the stripes coincides with the tilting-ordered regions. By their origin, the boundaries between the stripes should be atomically sharp.

cond-mat.supr-con↗

arXiv2018

Multiple electronic components and Lifshitz transitions by oxygen wires formation in layered cuprates and nickelates

There is a growing compelling experimental evidence that a quantum complex matter scenario made of multiple electronic components, and competing quantum phases is needed to grab the key physics of high critical temperature (Tc) superconductivity in layered cuprates. While it is known that defects self-organization controls Tc, the mechanism remains an open issue. Here we focus on the theoretical prediction of the multi-band electronic structure and the formation of broken Fermi surfaces generated by the self-organization of oxygen interstitials O-i atomic wires in the spacer layers in HgBa2CuO4+y, La2CuO4+y and La2NiO4+y, by means of self-consistent Linear Muffin-Tin Orbital (LMTO) calculations. The electronic structure of a first phase of ordered O-i atomic wires and of a second glassy phase made of disordered O-i impurities have been studied through supercell calculations. We show the common features of the influence of O-i wires in the electronic structure in three type of materials. The ordering of O-i into wires lead to a separation of the electronic states between the O-i ensemble and the rest of the bulk. The wires formation produce first quantum confined localized states near the wire which coexist with second delocalized states in the Fermi-surface (FS) of doped cuprates. In this new scenario for high Tc superconductivity, Kitaev wires with Majorana bound states are proximity-coupled to a 2D d-wave superconductor in cuprates.

cond-mat.supr-con↗

arXiv2018

Effect of CuO2 lattice strain on the electronic structure and properties of high-Tc cuprate family

Doping and strain dependences of the electronic structure of the CuO6-octahedra layer within LDA+GTB method in the frameworks of six-band p-d model are calculated. Band structure and Fermi surface of the quasiparticle excitations in the effective Hubbard model are characterized by inhomogeneous distribution of the k-dependent spectral weight. Doping results in reconstruction of the band structure, redistribution of the spectral weight over dispersion surface and reconstruction of Fermi surface from small hole pockets in the underdoped region to large hole contour in the overdoped region through two quantum phase transitions (QPT). Strain increasing leads to displacement of the valence and conductivity bands, bandwidths decreasing and shift of the concentrations corresponding to QPTs. Strain dependences of the antiferromagnetic exchange coupling and DOS at the Fermi level determining superconducting temperature Tc are obtained. Effective exchange coupling in the equation for Tc demonstrates monotonic strain dependence.

cond-mat.str-el↗

arXiv2018

VUV Pump and probe of phase separation and oxygen interstitials in La2NiO4+y using spectromicroscopy

While it is known that strongly correlated transition metal oxides described by multi-band Hubbard model show microscopic multiscale phase separation little is known on the possibility to manipulate them with vacuum ultraviolet (VUV) 27 eV lighting. We have investigated the photo-induced effects of VUV illumination of a super-oxygenated La2NiO4+y single crystal by means of scanning photoelectron microscopy. VUV light exposure induces the increase of the density of states (DOS) in the binding energy range around Eb =1.4 eV below EF. The photo-induced states in this energy region have been predicted as due to clustering of oxygen interstitials by band structure calculations for large supercell of La2CuO4.125. We finally show that it possible to generate and manipulate oxygen rich domains by VUV illumination as it was reported for X-ray illumination of La2CuO4+y. This phenomenology is assigned to oxygen-interstitials ordering and clustering by photo-illumination forming segregated domains in the La2NiO4+y surface

cond-mat.str-el↗

arXiv2018

Anisotropic thermal expansion of p-Terphenyl: a self-assembled supramolecular array of poly-p-phenyl nanoribbons

The recent discovery of superconductivity in a metallic aromatic hydrocarbon, alkali-doped p-Terphenyl, has attracted considerable interest. The critical temperature Tc ranges from few to 123 K, the record for organic superconductors, due to uncontrolled competition of multiple phases and dopant concentration. In the proposed mechanism of Fano resonance in a superlattice of quantum wires with coexisting polarons and Fermi particles, the lattice properties play a key role. Here we report a study of the temperature evolution of the parent compound p-Terphenyl crystal structure proposed to be made of a self-assembled supramolecular network of nanoscale nanoribbons. Using temperature dependent synchrotron radiation x-ray diffraction we report the anisotropic thermal expansion in the ab plane, which supports the presence of a nanoscale network of one-dimensional nanoribbons running in the b-axis direction in the P21/a structure. Below the enantiotropic phase transition at 193 K the order parameter of the C-1 structure follows a power law behaviour with the critical exponent 0.34 and the thermal expansion of the a-axis and b-axis show major changes supporting the formation of a two-dimensional bonds network. The large temperature range of the orientation fluctuations in a double well potential of the central phenyl has been determined.

cond-mat.supr-con↗

arXiv2018

Lifshitz transitions in multi-band Hubbard models for topological superconductivity in complex quantum matter

How the macroscopic quantum coherence can resist to the decoherence attacks of high temperature is a major challenge for the science of the 21st century. Superstripes 2017 conference held in Ischia on June 2017 has been focused on the new physics of high $T_c$ superconductors made of complex quantum matter. Today the standard model of high $T_c$ superconductivity which grabs the physics of complex quantum matter is the multi-band Hubbard model where the dome of $T_c$ occurs by driving the chemical potential in the proximity of a topological Lifshitz transition. The multi-gap superconductivity in the $T_c$ dome is driven by exchange interaction between a condensate in the BEC-BCS crossover which coexists with second BCS condensates. The proximity to Lifshitz transitions in correlated electronic systems gives the ubiquitous arrested phase separation observed in all high temperature superconductors. Non Euclidean filamentary hyperbolic geometry is needed for the space description of superstripes textures produced by the coexistence of short range CDW puddles, hole poor SDW puddles and self organized dopants rich puddles. A road map to room temperature superconductors in particular organic compounds made of superlattices of quantum wires driven by Fano resonances with one of the condensates in the BEC-BCS crossover has been proposed.

cond-mat.supr-con↗

arXiv2017

Local noncentrosymmetric structure of Bi2Sr2CaCu2O8+y by X-ray magnetic circular dichroism at Cu K-edge XANES

The two-dimensional Bi2Sr2CaCu2O8+y (Bi2212), the most studied prototype cuprate superconductor, is a lamellar system made of a stack of two-dimensional corrugated CuO2 bilayers separated by Bi2O2+ySr2O2 layers. While the large majority of theories, proposed to interpret unconventional high Tc superconductivity in Bi2Sr2CaCu2O8+y, assume a centrosymmetric tetragonal CuO2 lattice for the [CuO2]Ca[CuO2] bilayer here we report new compelling results providing evidence for local noncentrosymmetric structure at the Cu site. We have measured polarized Cu K-edge XANES (x-ray absorption near edge structure) and the K-edge X-ray magnetic circular dichroism (XMCD) of a Bi2212 single crystal near optimum doping. The Cu K edge XMCD signal was measured at ID12 beamline of ESRF with the k-vector of x-ray beam parallel to c-axis i.e. with the electric field of x-ray beam E//ab, using a 17 T magnetic field parallel to the c-axis of a Bi2212 single crystal. Numerical simulations of the XMCD signal of Bi2212 by multiple scattering theory have shown agreement with the experimental XMCD signal only for the local structure with noncentrosymmetric Bb2b space group of Bi2Sr2CaCu2O8+y.

cond-mat.supr-con↗

arXiv2017

Nanoscale correlated disorder in out-of-equilibrium myelin ultrastructure

Ultrastructural fluctuations at nanoscale are fundamental to assess properties and functionalities of advanced out-of-equilibrium materials. We have taken myelin as a model of supramolecular assembly in out-of-equilibrium living matter. Myelin sheath is a simple stable multi-lamellar structure of high relevance and impact in biomedicine. Although it is known that myelin has a quasi-crystalline ultrastructure there is no information on its fluctuations at nanoscale in different states due to limitations of the available standard techniques. To overcome these limitations, we have used Scanning micro X-ray Diffraction, which is a non-invasive probe of both reciprocal and real space to visualize statistical fluctuations of myelin order of the sciatic nerve of Xenopus Laevis. The results show that the ultrastructure period of the myelin is stabilized by large anti-correlated fluctuations at nanoscale, between hydrophobic and hydrophilic layers. The ratio between the total thickness of hydrophilic and hydrophobic layers defines the conformational parameter, which describes the different states of myelin. Our key result is that myelin in its out-of-equilibrium functional state fluctuates point-to-point between different conformations showing a correlated disorder described by a Levy distribution. As the system approaches the thermodynamic equilibrium in an aged state the disorder loses its correlation degree and the structural fluctuation distribution changes to Gaussian. In a denatured state at low pH, it changes to a completely disordered stage. Our results clarify also the degradation mechanism in biological systems by associating these states with variation of the ultrastructural dynamic fluctuations at nanoscale.

physics.bio-ph↗

arXiv2017

Electronic structure of HgBa$_2$CuO$_{4+δ}$ with self-organized interstitial oxygen wires in the Hg spacer planes

While recent experiments have found that at optimum doping for the highest critical temperature in HgBa$_2$CuO$_{4+y}$ (Hg1201) the oxygen interstitials (O-i) are not homogeneously distributed but form one-dimensional atomic wires, there are no available information of its electronic structure considering self-organized O-i atomic wires. Here we report the calculated electronic structure of HgBa$_2$CuO$_{4+y}$ where oxygen interstitials form atomic wires along (1,0,0) crystal direction in the Hg layer. We find that at optimum doping for superconductivity the chemical potential is tuned near an electronic topological Lifshitz transition for the appearing of a second quasi 1D Fermi surface. A $first$ large Fermi surface coexists with a $second$ incipient quasi one dimensional (1D) Fermi surface related with atomic wires of oxygen interstitials. Increasing oxygen doping the chemical potential is driven to the band edge of the $second$ 1D-band giving a peak in the density-of-states. The new 1D electronic states are confined near the oxygen interstitial wires with a small spread only on nearby sites. Spin-polarized calculations show that the magnetic response is confined in the oxygen-poor domains free of oxygen interstitials wires and it is quite insensitive to the density of O-i wires.

cond-mat.supr-con↗

arXiv2017

Correlated disorder in myelinated axons orientational geometry and structure

While the ultrastructure of the myelin has been considered to be a quasi-crystalline stable system, nowadays its multiscale complex dynamics appears to play a key role for its functionality, degeneration and repair processes following neurological diseases and trauma. In this work, we have investigated the axons interactions associated to the nerve functionality, measuring the spatial distribution of the orientational fluctuations of axons in a Xenopus Laevis sciatic nerve. At this aim, we have used Scanning micro X-ray Diffraction (SmXRD), a non-invasive already applied to other heterogeneous systems presenting complex geometries from microscale to nanoscale. We have found that the orientational spatial fluctuations of fresh axons show a correlated disorder described by Levy flight distribution. Thus, we have studied how this correlated disorder evolves during the degeneration of the nerve. Our results show that the spatial distribution of axons orientational fluctuations in unfresh, aged nerve loose the correlated disorder assuming a randomly disordered behaviour. This work allows a deeper understanding of nerve states and paves the way to study other materials and biomaterials with the same technique to detect and to characterize their states and supramolecular structure, associated with dynamic structural changes at the nanoscale and mesoscale.

q-bio.QM↗

arXiv2017

X-rays writing/reading of Charge Density Waves in the CuO2 plane of a simple cuprate superconductor

It is now well established that superconductivity in cuprates competes with charge modulations giving electronic phase separation at a nanoscale. More specifically, superconducting electronic current takes root in the available free space left by electronic charge ordered domains, called charge density wave (CDW) puddles. This means that CDW domain arrangement plays a fundamental role in the mechanism of high temperature superconductivity in cuprates. Here we report about the possibility of controlling the population and spatial organization of the charge density wave puddles in a single crystal La2CuO4+y through X - ray illumination and thermal treatments. We apply a pump - probe method based on X - ray illumination as pump and X - ray diffraction as a probe setting a writing and reading procedure of CDW puddles. Our findings are expected to allow new routes for advanced design and manipulation of superconducting pathways in new electronics.

cond-mat.supr-con↗

arXiv2017

Many body quantum physics in XANES of highly correlated materials, mixed valence oxides and high temperature superconductors

The x-ray absorption near edge structure (XANES), developed in these last 40 years using synchrotron radiation, is a unique tool probing electronic correlations in complex systems via quantum many body final state effects. Multi electron excitations have been observed first in the sixties in x-ray absorption spectra of atoms and later in molecules and solids. The applications of XANES many body final states to probe unique features of electronic correlation in heavy fermions, mixed valence systems, mixed valence oxides and high temperature superconductors are discussed.

cond-mat.str-el↗