A5042543177- Physics of Superconductivity and Magnetism
- Advanced Condensed Matter Physics
- Iron-based superconductors research
- Magnetic and transport properties of perovskites and related materials
- Electronic and Structural Properties of Oxides
- Rare-earth and actinide compounds
- Superconductivity in MgB2 and Alloys
- Quantum and electron transport phenomena
- Magnetic properties of thin films
- Theoretical and Computational Physics
- Topological Materials and Phenomena
- Cold Atom Physics and Bose-Einstein Condensates
- Corporate Taxation and Avoidance
- Lipid Membrane Structure and Behavior
- Quantum, superfluid, helium dynamics
- High-pressure geophysics and materials
- Surface and Thin Film Phenomena
- RNA Research and Splicing
- Superconducting Materials and Applications
- Diffusion and Search Dynamics
- 2D Materials and Applications
- Advanced Thermodynamics and Statistical Mechanics
- Molecular Junctions and Nanostructures
- ZnO doping and properties
- Advanced Electron Microscopy Techniques and Applications
Leibniz Institute for Solid State and Materials Research
2019-2025
University of Naples Federico II
2024-2025
Harvard University
2017-2023
Rome International Center for Materials Science
2013-2016
University of Twente
2013-2016
Scuola Normale Superiore
2015-2016
Istituto Nanoscienze
2015-2016
Sapienza University of Rome
2008-2012
European Synchrotron Radiation Facility
2012
Advanced synchrotron radiation focusing down to a size of 300 nm has been used visualize nanoscale phase separation in the K${}_{0.8}$Fe${}_{1.6}$Se${}_{2}$ superconducting system using scanning nanofocus single-crystal x-ray diffraction. The results show an intrinsic single crystals at $T$ 520 K, revealing coexistence (i) magnetic characterized by expanded lattice with superstructures due Fe vacancy ordering and (ii) nonmagnetic in-plane compressed lattice. spatial distribution two phases K...
Twisted interfaces between stacked van der Waals (vdW) cuprate crystals present a platform for engineering superconducting order parameters by adjusting stacking angles. Using cryogenic assembly technique, we construct twisted vdW Josephson junctions (JJs) at atomically sharp Bi2Sr2CaCu2O8+x crystals, with quality approaching the limit set intrinsic JJs. Near 45° twist angle, observe fractional Shapiro steps and Fraunhofer patterns, consistent existence of two degenerate ground states...
A proposed new design of superconducting qubits uses Josephson junctions made with a high-${T}_{c}$ $d$-wave superconductor overlaying conventional $s$-wave to increase their coherence time and stability in the presence noise.
Motivated by the recent proposals for unconventional emergent physics in twisted bilayers of nodal superconductors, we study peculiarities Josephson effect at interface between $d$-wave superconductors. We demonstrate that clean interfaces with a twist angle $\theta_0$ range $0^\circ<\theta_0<45^\circ$ critical current can exhibit nonmonotonic temperature dependence maximum nonzero as well complex on low temperatures. The former is shown to arise quite generically due contributions momenta...
Oxide heterostructures often exhibit unusual physical properties that are absent in the constituent bulk materials. Here, we report an atomically sharp transition to a ferromagnetic phase when polar antiferromagnetic LaMnO3 (001) films grown on SrTiO3 substrates. For thickness of six unit cells or more, film abruptly becomes over its entire area, which is visualized by scanning superconducting quantum interference device microscopy. The explained terms electronic reconstruction originating...
Resonances in the superconducting properties, a regime of crossover from BCS to mixed Bose-Fermi superconductivity, are investigated two-band superconductor where chemical potential is tuned near band edge second mini-band generated by quantum confinement effects. The shape resonances at T=0 gaps (belonging class Feshbach-like resonances) manifested interference effects gap first large Fermi surface when proximity mini-band. case superlattice wells considered and amplification...
Temperature dependent single-crystal x-ray diffraction (XRD) in transmission mode probing the bulk of newly discovered K0.8Fe1.6Se2 superconductor (Tc = 31.8 K) using synchrotron radiation is reported. A clear evidence intrinsic phase separation at 520 K between two competing phases, (i) a first majority magnetic with ThCr2Si2-type tetragonal lattice modulated by iron vacancy ordering and (ii) minority non-magnetic having an in-plane compressed volume weak superstructure, The XRD peaks due...
Electronic functionalities in materials from silicon to transition metal oxides are a large extent controlled by defects and their relative arrangement. Outstanding examples the of copper, where defect order is correlated with high superconducting temperatures. The oxygen can be highly inhomogeneous, even "optimal" samples, which raises question nature sample regions does not exist but nonetheless form "glue" binding ordered together. Here we use scanning X-ray microdiffraction (with beam...
High-temperature cuprate superconductors based van der Waals (vdW) heterostructures hold high technological promise. One of the obstacles hindering their progress is detrimental effect disorder on properties vdW-devices-based Josephson junctions (JJs). Here, a new method fabricating twisted vdW made Bi2 Sr2 CuCa2 O8+δ , crucially improving JJ characteristics and pushing them up to those intrinsic JJs in bulk samples, reported. The combines cryogenic stacking using solvent-free stencil mask...
We fabricate van der Waals heterostructure devices using few unit cell thick Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ for magnetotransport measurements. The superconducting transition temperature and carrier density in atomically thin samples can be maintained to close that of the bulk samples. As sample, sign Hall conductivity is found opposite normal state near but with a drastic enlargement region reversal temperature-magnetic field phase diagram as thickness decreases. Quantitative analysis...
In the framework of a two-band model, we study phase-separation regime different kinds strongly correlated charge carriers as function energy splitting between two sets bands. The narrow (wide) band simulates more localized (more delocalized) type carriers. By assuming that internal chemical pressure on ${\text{CuO}}_{2}$ layer due to interlayer mismatch controls states, theoretical predictions are able reproduce phase separation at doping higher than 1/8 in experimental...
High-Tc superconductivity in FeAs-based (pnictide) multilayers, evading temperature decoherence effects a quantum condensate, is assigned to Feshbach resonance (also called shape resonance) the exchange-like interband pairing. The switched on by tuning chemical potential at an electronic topological transition (ETT) near band edge, where Fermi surface topology of one subbands changes from one-dimensional (1D) two-dimensional (2D) topology. We show that realized changing (i) misfit strain...
We have used scanning micro x-ray diffraction to characterize different phases in superconducting ${\mathrm{K}}_{x}{\mathrm{Fe}}_{2\ensuremath{-}y}{\mathrm{Se}}_{2}$ as a function of temperature, unveiling the thermal evolution across transition temperature (${T}_{c}\ensuremath{\sim}32$ K), phase separation (${T}_{ps}\ensuremath{\sim}520$ and iron-vacancy order (${T}_{vo}\ensuremath{\sim}580$ K). In addition ordered tetragonal magnetic orthorhombic metallic minority filamentary phase, we...
Twisted interfaces between stacked van der Waals cuprate crystals enable tunable Josephson coupling in-plane anisotropic superconducting order parameters. Employing a novel cryogenic assembly technique, we fabricate junctions with an atomically sharp twisted interface Bi2Sr2CaCu2O8+x crystals. The critical current density sensitively depends on the twist angle, reaching maximum value comparable to that of intrinsic at small twisting angles, and is suppressed by almost 2 orders magnitude yet...
The multigap superconductivity modulated by quantum confinement effects in a superlattice of wells is presented.Our theoretical BCS approach captures the low-energy physics shape resonance superconducting gaps when chemical potential tuned near Lifshitz transition.We focus on case weak Cooper-pairing coupling channels and strong pair exchange interaction driven repulsive Coulomb that allows to use theory weakcoupling regime neglecting retardation like condensates ultracold gases.The...
An array of superconducting islands placed on a normal metal film offers tunable realization nanopatterned superconductivity. This system enables investigation the nature competing vortex states and phase transitions between them. A square creates eggcrate potential in which magnetic field-induced vortices are frozen into insulator. We observed insulator-vortex transition driven by applied electric current determined critical exponents that coincided with those for thermodynamic liquid-gas...
The arrested nanoscale phase separation in a two-band Hubbard model for strongly correlated charge carriers is shown to occur particular range vicinity of the topological Lifshitz transition, where Fermi energy crosses bottom narrow band and new sheet surface related second comes into play. We determine diagram this as function two variables, carrier density shift between chemical potential band. In diagram, we first line quantum critical points transition find criteria electronic resulting...
Thermoelectric transport has been widely used to study Abrikosov vortex dynamics in unconventional superconductors. However, only a few thermoelectric studies have conducted near the dimensional crossover that occurs when vortex-vortex interaction length scale becomes comparable sample size. Here we report effects of finite size on dissipation mechanisms Nernst effect optimally doped $\text{Bi}_{2}\text{Sr}_{2}\text{CaCu}_{2}\text{O}_{8+x}$ high-temperature superconductor, down atomic limit....
A two-band model is used to study the phase separation in systems with different kinds of strongly correlated charge carrier, a special emphasis on cuprate superconductors near optimum doping. We show that such system can decompose into two metallic-like phases more and less localized carriers. This controlled by energy splitting between bands. In superconductors, this be related internal chemical pressure CuO2 layer due interlayer mismatch. The interplay surface nanoscale inhomogeneities...
Using scanning micro-x-ray diffraction we report a mixed real and reciprocal space visualization of the spatial heterogeneity lattice incommensurate supermodulation in single crystal Bi${}_{2}$Sr${}_{2}$CaCu${}_{2}$O${}_{8+y}$ with ${T}_{c}$ = 84 K. The mapping shows an amplitude distribution large fluctuations at microscale \ensuremath{\sim}50% variation. angular a-$b$ plane chiral symmetry, forming left-handed oriented striped pattern. correlation is well described by compressed...
High-temperature superconductivity (HTS) emerges in quite different electronic materials: cuprates, diborides, and iron-pnictide superconductors. Looking for unity the diversity we find all these materials a common lattice architecture: they are practical realizations of heterostructures at atomic limit made superlattices metallic active layers intercalated by spacers as predicted 1993 one us. The multilayer architecture is key feature presence topological transitions where Fermi surface...