A5052366646- Physics of Superconductivity and Magnetism
- Iron-based superconductors research
- Advanced Condensed Matter Physics
- Rare-earth and actinide compounds
- Magnetic and transport properties of perovskites and related materials
- Superconductivity in MgB2 and Alloys
- High-pressure geophysics and materials
- Electronic and Structural Properties of Oxides
- Magnetic properties of thin films
- Corporate Taxation and Avoidance
- Advanced Thermoelectric Materials and Devices
- Inorganic Chemistry and Materials
- Quantum Electrodynamics and Casimir Effect
- Superconducting Materials and Applications
- 2D Materials and Applications
- Advanced Chemical Physics Studies
- Tardigrade Biology and Ecology
- Advancements in Battery Materials
- Chalcogenide Semiconductor Thin Films
- Transition Metal Oxide Nanomaterials
- Surface and Thin Film Phenomena
- Cosmology and Gravitation Theories
- X-ray Spectroscopy and Fluorescence Analysis
- Boron and Carbon Nanomaterials Research
- Intellectual Capital and Performance Analysis
Sapienza University of Rome
2016-2025
Istituto Nazionale di Fisica Nucleare, Sezione di Roma I
2001-2024
Istituto Nazionale di Fisica Nucleare
1996-2022
Aix-Marseille Université
2015
The University of Tokyo
2010-2013
Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati
2008
Istituto Nazionale per la Fisica della Materia
1998-2002
University of Rajasthan
1989-2000
MAX IV Laboratory
1993
Lund University
1993
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...
We report Mn $K$-edge extended x-ray absorption fine structure spectra on ${\mathrm{La}}_{0.75}{\mathrm{Ca}}_{0.25}{\mathrm{MnO}}_{3}$ up to high momentum transfer across the metal-insulator $(M\ensuremath{-}I)$ transition. The data show compelling evidence for (i) large or intermediate Jahn-Teller polarons (IJTP), characterized by an anomalous longer Mn-O bond $(\ensuremath{\Delta}R\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.09\AA{})$ in metallic phase $(T<170\mathrm{K})$, and (ii)...
We show that finite temperature variational cluster approximation (VCA) calculations on an extended Falicov-Kimball model can reproduce angle-resolved photoemission spectroscopy (ARPES) results ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ across a semiconductor-to-semiconductor structural phase transition at 325 K. demonstrate the characteristic dependence of flat-top valence band observed by ARPES is reproduced VCA calculation realistic for excitonic insulator only when strong fluctuation taken...
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...
The goal of the Archimedes experiment is to investigate role interaction between vacuum fluctuations and gravitational field. This will be possible thanks a high sensitivity cryogenic balance installed in SarGrav laboratory Sos Enattos mine (Sardinia), Italian candidate site for third generation wave observatory Einstein Telescope. measure small weight variations induced two temperature superconductors that have property “trapping” or “expelling” energy when their temperatures are greater...
We report topology of the Fermi surface ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ superconducting system at optimum doping determined by sequential angle-scanning photoemission combined with high intensity synchrotron radiation. The has a pseudogap around $(\ensuremath{\pi},0)$ as in underdoped samples, showing missing segments near $M$ points, and shadow bands $(0.5\ensuremath{\pi},0.5\ensuremath{\pi})$ equivalent locations. $k$ dependence...
We have performed Ce $L_3$-edge x-ray absorption spectroscopy (XAS) measurements on CeO$_{1-x}$F$_x$BiS$_2$, in which the superconductivity of BiS$_2$ layer and ferromagnetism CeO$_{1-x}$F$_x$ are induced by F-doping, order to investigate impact F-doping local electronic lattice structures. The XAS spectrum CeOBiS$_2$ exhibits coexistence $4f^1$ (Ce$^{3+}$) $4f^0$ (Ce$^{4+}$) state transitions revealing mixed valency this system. spectral weight decreases with completely disappears for...
Temperature-dependent polarized Cu K-edge x-ray absorption has been used to investigate local structural distortions in the ${\mathrm{CuO}}_{2}$ plane of ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ system. The Cu-O pair distribution shows presence a minority phase containing ${\mathrm{CuO}}_{6}$ octahedra characterized by shorter Cu-O(apical) bond (\ensuremath{\Delta}R\ensuremath{\sim}-0.1 \AA{}) and two longer Cu-O(planar) bonds...
The modulated structure of the ${\mathrm{CuO}}_{2}$ plane in ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathit{y}}$ superconductor has been solved by Cu K-edge anomalous x-ray diffraction. displacement ions along c axis shows largest amplitude and anharmonic character. results show flat stripes lattice width L=15.5 \AA{} with long Cu-Bi distances that are separated bent shorter distances. In each bilayer a first layer close to second layer, suppressing...
The Cu-O pair-distribution function in a ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathit{y}}$ superconductor has been measured by polarized Cu K-edge extended x-ray-absorption fine structure at T${\mathit{T}}_{\mathit{c}}$. results show an anomalous long (planar) distance, 1.96 \AA{}, assigned to distorted ${\mathrm{CuO}}_{2}$ stripes of width W intercalated with undistorted L. From the measurement L=15\ifmmode\pm\else\textpm\fi{}0.5 \AA{} we have...
A very large oxygen-isotope shift of the charge-stripe ordering temperature in high-temperature superconductors La2-xSrxCuO4 has been observed using x-ray absorption spectroscopy, a fast (~10-15 seconds) and local probe (~5 A). Upon replacing 16O with 18O, La1.94Sr0.06CuO4 increases from about 110 K to 180 K. The present results provide compelling evidence for strong electron-phonon interaction this compound, thus place important constraints on microscopic origin stripe formation.
Local structure of ${\text{FeSe}}_{1\ensuremath{-}x}{\text{Te}}_{x}$ has been studied by extended x-ray absorption fine-structure (EXAFS) measurements as a function temperature. Combination Se and $\text{Fe}\text{ }K$ edge EXAFS permitted to quantify the local interatomic distances their mean-square relative displacements. The Fe-Se Fe-Te bond lengths in ternary system are found be very different from average crystallographic Fe-Se/Te distance, almost identical for binary FeSe FeTe systems,...
We have studied electronic structure of triangular lattice Ir$_{1-x}$Pt$_x$Te$_2$ superconductor using photoemission spectroscopy and model calculations. Ir $4f$ core-level spectra show that $5d$ $t_{2g}$ charge modulation established in the low temperature phase IrTe$_2$ is suppressed by Pt doping. This observation indicates suppression related to emergence superconductivity. Valence-band suggest accompanied orbital reconstruction. Based on results calculations, we argue orbitally-induced...
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...
The experimental determination of the scaling superconducting critical temperature ${(T}_{c})$ vs Fermi ${(T}_{f})$ holes in boron \ensuremath{\sigma} subband is presented. level has been tuned near ``shape resonance,'' i.e., two- to three-dimensional crossover surface by changing Al/Mg content ${\mathrm{Al}}_{1\ensuremath{-}x}{\mathrm{Mg}}_{x}{\mathrm{B}}_{2}.$ product ${k}_{f}{\ensuremath{\xi}}_{0}$ wave vector ${(k}_{f})$ times Pippard coherence length $({\ensuremath{\xi}}_{0}),$ that a...
We show the key role of elastic local strain (or micro-strain) ε CuO2 lattice in phase diagram cuprate superconductors. The superconducting critical temperature Tc(δ, ε) is shown to be a function two variables, doping δ and microstrain ε.
Fe K-edge and Se x-ray absorption near edge structure (XANES) measurements are used to study the FeSe(1 - x)Te(x) electronic of chalcogenides. An intense pre-edge peak due 1s --> 3d (and admixed Se/Te p states) is observed, showing substantial change with Te substitution polarization. The main white line in XANES 4p transition appears similar one expected for Se(2-) systems changes substitution. Polarization dependence reveals that unoccupied orbitals Fermi level have predominant p(x, y)...
We have studied the effect of RE substitution on structure and local atomic disorder in REO0.5F0.5BiS2 (RE = rare-earth) to understand their correlation with bulk superconductivity these materials. The mean size, affecting chemical pressure, has been varied two series namely Ce1-xNdxO0.5F0.5BiS2 Nd1-ySmyO0.5F0.5BiS2. lattice parameters evolve anomalously, showing an anisotropic shrinkage (elongation) c-axis (a-axis) isotropic expansion increasing size. Bi L3-edge extended X-ray absorption...
We have used Bi and Ce L3-edges extended x-ray absorption fine structure measurements to study local of CeO1−xFxBiS2 system as a function F-substitution. The both BiS2 active layer CeO1−xFx spacer changes systematically. in-plane Bi–S1 distance decreases (ΔRmax ∼ 0.08 Å) the out-of-plane Bi–S2 increases 0.12 with increasing F-content. On other hand, Ce-O/F 0.2 concomitant decrease Ce–S2 0.15 Å). Interestingly, is characterized by large disorder that results provide useful information on...