S. Lupi

Sapienza University of Rome, Roma, Latium, Italy

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Publications (216)492.72 Total impact

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    ABSTRACT: Amyloid and amyloid-like fibrils are a general class of protein aggregates and represent a central topic in life sciences for their involvement in several neurodegenerative disorders and their unique mechanical and supramolecular morphological properties. Both their biological role and their physical properties, including their high mechanical stability and thermodynamic inertia, are related to the structural arrangement of proteins in the aggregates at molecular level. Significant variations may exist in the supramolecular organization of the commonly termed cross-β structure that constitutes the amyloid core. In this context, a fine knowledge of the structural details in fibrils may give significant information on the assembly process and on possible ways of tuning or inhibiting it. Here we propose a simple method based on the combined use of Fourier Transform Infrared spectroscopy and Fourier Transform Raman spectroscopy to accurately reveal structural details in the fibrillar aggregates, side-chains exposure and intermolecular interactions. Interestingly, coupled analysis of mid-infrared spectra reveals antiparallel β-sheets orientation in ConA fibrils. We also report the comparison between THz absorption spectra of Concanavalin A in its native and fibrillar state at different hydration levels, allowing obtaining corroboration of peaks assignation in this range and information on the effect of amyloid supramolecular arrangement on the network dynamics of hydration water.
    Biophysical chemistry 02/2015; · 2.28 Impact Factor
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    ABSTRACT: One of the pivotal questions in the physics of high-temperature superconductors is whether the low-energy dynamics of the charge carriers is mediated by bosons with a characteristic timescale. This issue has remained elusive since electronic correlations are expected to dramatically speed up the electron-boson scattering processes, confining them to the very femtosecond timescale that is hard to access even with state-of-the-art ultrafast techniques. Here we simultaneously push the time resolution and the frequency range of transient reflectivity measurements up to an unprecedented level that enables us to directly observe the 16 fs build-up of the effective electron-boson interaction in hole-doped copper oxides. This extremely fast timescale is in agreement with numerical calculations based on the t-J model and the repulsive Hubbard model, in which the relaxation of the photo-excited charges is achieved via inelastic scattering with short-range antiferromagnetic excitations.
    01/2015;
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    ABSTRACT: Terahertz spectroscopy has vast potentialities in sensing a broad range of elementary excitations (e.g., collective vibrations of molecules, phonons, excitons, etc.). However, the large wavelength associated with terahertz radiation (about 300 μm at 1 THz) severely hinders its interaction with nano-objects, such as nanoparticles, nanorods, nanotubes and large molecules of biological relevance, practically limiting terahertz studies to macroscopic ensembles of these compounds, in the form of thick pellets of crystallized molecules or highly concentrated solutions of nanomaterials. Here we show that chains of terahertz dipole nanoantennas spaced by nanogaps of 20 nm allow retrieving the spectroscopic signature of a monolayer of cadmium selenide quantum dots, a significant portion of the signal arising from the dots located within the antenna nanocavities. A Fano-like interference between the fundamental antenna mode and the phonon resonance of the quantum dots is observed, accompanied by an absorption enhancement factor greater than one million. NETS can find immediate applications in terahertz spectroscopic studies of nanocrystals and molecules at extremely low concentrations. Furthermore, it shows a practicable route towards the characterization of individual nano-objects at these frequencies.
    Nano Letters 11/2014; · 13.03 Impact Factor
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    Plasmonics 10/2014; · 2.74 Impact Factor
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    ABSTRACT: We report an infrared spectroscopy study of a 200 nm thick FeSe$_{0.5}$Te$_{0.5}$ film grown on LaAlO$_3$ with T$_c$=13.7 K. We analyze the 20 K normal state absolute reflectance R$_N$ measured over a broad infrared range and the reflectance ratio R$_S$/R$_N$, R$_S$ being the superconducting state reflectance, measured at 6 K in the terahertz range down to 12 cm$^{-1}$. We show that the normal state model conductivity is given by two Drude components, one of which much broader and intense than the other. In the superconducting state, we find that a gap $\Delta$=37$\pm$3 cm$^{-1}$ opens up in the narrow Drude band only, while the broad Drude band results to be ungapped, at least in the explored spectral range. Our results show that only a two-band model can coherently describe both normal and superconducting state data.
    Superconductor Science and Technology 10/2014; 27(12). · 2.80 Impact Factor
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    ABSTRACT: A plasmonic analogue of electromagnetically induced transparency is activated and tuned in the terahertz (THz) range in asymmetric metamaterials fabricated from high critical temperature (Tc) superconductor thin films. The asymmetric design provides a near-field coupling between a superradiant and a subradiant plasmonic mode, which has been widely tuned through superconductivity and monitored by Fourier transform infrared spectroscopy. The sharp transparency window that appears in the extinction spectrum exhibits a relative modulation up to 50% activated by temperature change. The interplay between ohmic and radiative damping, which can be independently tuned and controlled, allows for engineering the electromagnetically induced transparency of the metamaterial far beyond the current state-of-the-art, which relies on standard metals or low-Tc superconductors.Keywords: superconductivity; electromagnetic-induced transparency; THz; dark mode; Fano resonance; tunable metamaterials
    ACS Photonics. 07/2014; 1(7):570-575.
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    ABSTRACT: The optical properties of a V4O7 single crystal have been investigated from the high temperature metallic phase down to the low temperature antiferromagnetic insulating one. The temperature dependent behavior of the optical conductivity across the metal-insulator transition (MIT) can be explained in a polaronic scenario. Charge carriers form strongly localized polarons in the insulating phase as suggested by a far-infrared charge gap abruptly opening at T_MIT = 237 K. In the metallic phase instead the presence of a Drude term is indicative of fairly delocalized charges with a moderately renormalized mass m* = 5m_e. The electronic spectral weight is almost recovered on an energy scale of 1 eV, which is much narrower compared to VO2 and V2O3 cases. Those findings suggest that electron-lattice interaction rather than electronic correlation is the driving force for V4O7 metal-insulator transition.
    07/2014;
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    ABSTRACT: Exploiting the localization and enhancement capabilities of terahertz resonant dipole nanoantennas coupled through nanogaps, we present an effective method to perform terahertz spectroscopy on an extremely small number of nano-objects.
    CLEO: Science and Innovations; 06/2014
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    ABSTRACT: Photosynthetic reaction centers develop a stable charge separated state upon illumination. To investigate the molecular vibrations associated with the illuminated state of a reaction center we recorded terahertz absorption spectra of the photosynthetic reaction center from Rhodobacter sphaeroides in the dark and upon illumination and observed a small, but significant THz absorption increase in the 20 to 130 cm−1 spectral region. Reaction centers show very similar terahertz absorption increase when solubilized in detergents and in a lipidic sponge phase indicating that the nature of the bulk solvent has limited influence on the vibrational spectrum. The absorption change of the isolated LM subunit is very similar to that of the intact reaction center. Through temperature control experiments we show that 89% of the absorption change is likely attributed to the non-thermal activation of the protein molecules. These results indicate that picosecond molecular vibrations change primarily in the cofactors and/or in the evolutionary conserved core of the reaction center upon illumination, whereas the nuclear motions of the H-subunit and the bulk solvent have limited impact on the terahertz spectral changes.
    RSC Advances 05/2014; 4(49):25502-25509. · 3.71 Impact Factor
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    ABSTRACT: It has been recently reported (S. Lee et al., Nature Materials 12, 392, 2013) that superlattices where layers of the 8% Co-doped BaFe2As2 superconducting pnictide are intercalated with non superconducting ultrathin layers of either SrTiO3 or of oxygen-rich BaFe2As2, can be used to control flux pinning, thereby increasing critical fields and currents, without significantly affecting the critical temperature of the pristine superconducting material. However, little is known about the electron properties of these systems. Here we investigate the electrodynamics of these superconducting pnictide superlattices in the normal and superconducting state by using infrared reflectivity, from THz to visible range. We find that multi-gap structure of these superlattices is preserved, whereas some significant changes are observed in their electronic structure with respect to those of the original pnictide. Our results suggest that possible attempts to further increase the flux pinning may lead to a breakdown of the pnictide superconducting properties.
    Applied Physics Letters 04/2014; 104(22). · 3.52 Impact Factor
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    ABSTRACT: This paper describes the scientific aims and potentials as well as the preliminary technical design of IRIDE, an innovative tool for multi-disciplinary investigations in a wide field of scientific, technological and industrial applications. IRIDE will be a high intensity “particles factory”, based on a combination of high duty cycle radio-frequency superconducting electron linacs and of high energy lasers. Conceived to provid eunique research possibilities for particle physics, for condensed matter physics,chemistry and material science, for structural biology and industrial applications, IRIDE will open completely new research possibilities and advance our knowledge in many branches of science and technology. IRIDE is also supposed to be realized in subsequent stages of development depending on the assigned priorities.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 03/2014; 740:138-146. · 1.32 Impact Factor
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    ABSTRACT: At SPARC-LAB, we have installed an Electro-Optic Sampling (EOS) experiment for single shot, non-destructive measurements of the longitudinal distribution charge of individual electron bunches. The profile of the electron bunch field is electro-optically encoded into a Ti:Sa laser, having 130 fs (rms) pulse length, directly derived from the photocathode's laser. The bunch profile information is spatially retrieved, i.e., the laser crosses with an angle of 30° with respect to the normal to the surface of EO crystal (ZnTe, GaP) and the bunch longitudinal profile is mapped into the laser's transverse profile. In particular, we used the EOS for a single-shot direct visualization of the time profile of a comb-like electron beam, consisting of two bunches, about 100 fs (rms) long, sub-picosecond spaced with a total charge of 160 pC. The electro-optic measurements (done with both ZnTe and GaP crystals) have been validated with both RF Deflector (RFD) and Michelson interferometer measurements.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/2014; 740. · 1.32 Impact Factor
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    ABSTRACT: Optical pulses at THz and mid-infrared frequencies tuned to specific vibrational resonances modulate the lattice along chosen normal mode coordinates. In this way, solids can be switched between competing electronic phases and new states are created. Here, we use vibrational modulation to make electronic interactions (Hubbard-U) in Mott-insulator time dependent. Mid-infrared optical pulses excite localized molecular vibrations in ET-F2TCNQ, a prototypical one-dimensional Mott-insulator. A broadband ultrafast probe interrogates the resulting optical spectrum between THz and visible frequencies. A red-shifted charge-transfer resonance is observed, consistent with a time-averaged reduction of the electronic correlation strength U. Secondly, a sideband manifold inside of the Mott-gap appears, resulting from a periodically modulated U. The response is compared to computations based on a quantum-modulated dynamic Hubbard model. Heuristic fitting suggests asymmetric holon-doublon coupling to the molecules and that electron double-occupancies strongly squeeze the vibrational mode.
    Scientific Reports 01/2014; 4:3823. · 5.08 Impact Factor
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    ABSTRACT: La1.8-xEu0.2SrxCuO4 (LESCO) is the member of the 214 family which exhibits the largest intervals among the structural, charge ordering (CO), magnetic, and superconducting transition temperatures. By using new dc transport measurements and data in the literature we construct the phase diagram of LESCO between x = 0.8 and 0.20. This phase diagram has been further probed in ac, by measuring the optical conductivity {\sigma}1({\omega}) of three single crystals with x = 0.11, 0.125, and 0.16 between 10 and 300 K in order to associate the extra-Drude peaks often observed in the 214 family with a given phase. The far-infrared peak we detect in underdoped LESCO is the hardest among them, survives up to room temperature and is associated with charge localization rather than with ordering. At the CO transition for the commensurate doping x = 0.125 instead the extra-Drude peak hardens and a pseudogap opens in {\sigma}1({\omega}), approximately as wide as the maximum superconducting gap of LSCO.
    10/2013;
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    ABSTRACT: It is widely recognized that a central role in conferring stability to the structure of proteins against misfolding and aggregation is played by the formation of oligomers. The case of insulin is prototypical in this respect: in our body it is stored up in stable inactive hexameric assemblies whereas only in its monomeric form it recovers the role of regulating carbohydrate and fat metabolism. In the present paper, exploiting the optimal coupling between FTIR spectroscopy and diamond anvil cell technique, we probe the stability of different insulin oligomeric forms under high pressure, namely over the ranges 0–15 kbar for water solution and 0–80 kbar for dry powder. Results obtained show different responses to volume compression for the different assemblies being the structure of monomers and dimers remarkably more affected by compression than hexamers. Moreover by comparing the results obtained using water solution and dry powder we were able to draw important considerations about the role of water in the high pressure unfolding processes.
    Journal of Molecular Structure 10/2013; 1050:159-165. · 1.60 Impact Factor
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    ABSTRACT: The magnetically driven metal-insulator transition (MIT) was predicted by Slater in the fifties. Here a long-range antiferromagnetic (AF) order can open up a gap at the Brillouin electronic band boundary regardless of the Coulomb repulsion magnitude. However, while many low-dimensional organic conductors display evidence for an AF driven MIT, in three-dimensional (3D) systems the Slater MIT still remains elusive. We employ terahertz and infrared spectroscopy to investigate the MIT in the NaOsO3 3D antiferromagnet. From the optical conductivity analysis we find evidence for a continuous opening of the energy gap, whose temperature dependence can be well described in terms of a second order phase transition. The comparison between the experimental Drude spectral weight and the one calculated through Local Density Approximation (LDA) shows that electronic correlations play a limited role in the MIT. All the experimental evidence demonstrates that NaOsO3 is the first known 3D Slater insulator.
    Scientific Reports 10/2013; 3:2990. · 5.08 Impact Factor
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    ABSTRACT: We present an experimental study of subwavelength hole arrays in thin metal films employed as surface-enhanced optical sensors operating in the mid-infrared. The extremely narrow surface plasmon polariton spectral resonances are fitted to an analytical Fano interference model in the wavelength range 2–10 μm. In general, the resonance frequency shifts after deposition of few-molecule layers (3.2–24 nm thickness) according to electrodynamic polarization models, hence allowing for label-free sensing. The absolute value of the shift is shown to depend on the overlap between the electric field distribution of the specific surface plasmon mode and the molecular layer, as verified by electromagnetic simulations. Biochemical sensor application is finally demonstrated by determining, from a single mid-infrared measurement, both the thickness and the absorption spectrum of phospholipid monolayers and trilayers, obtained by liposome adsorption.
    The Journal of Physical Chemistry C 09/2013; 117(37):19119–19126. · 4.84 Impact Factor
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    ABSTRACT: A new facility named SPARC_LAB has been recently launched at the INFN National Laboratories in Frascati, merging the potentialities of the former projects SPARC and PLASMONX. We describe in this paper the status and the future perspectives at the SPARC_LAB facility.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 08/2013; 309:183-188. · 1.19 Impact Factor
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    ABSTRACT: This report describes the scientific aims and potentials as well as the preliminary technical design of IRIDE, an innovative tool for multi-disciplinary investigations in a wide field of scientific, technological and industrial applications. IRIDE will be a high intensity 'particle factory', based on a combination of a high duty cycle radio-frequency superconducting electron linac and of high energy lasers. Conceived to provide unique research possibilities for particle physics, for condensed matter physics, chemistry and material science, for structural biology and industrial applications, IRIDE will open completely new research possibilities and advance our knowledge in many branches of science and technology. IRIDE will contribute to open new avenues of discoveries and to address most important riddles: What does matter consist of? What is the structure of proteins that have a fundamental role in life processes? What can we learn from protein structure to improve the treatment of diseases and to design more efficient drugs? But also how does an electronic chip behave under the effect of radiations? How can the heat flow in a large heat exchanger be optimized? The scientific potential of IRIDE is far reaching and justifies the construction of such a large facility in Italy in synergy with the national research institutes and companies and in the framework of the European and international research. It will impact also on R&D work for ILC, FEL, and will be complementarity to other large scale accelerator projects. IRIDE is also intended to be realized in subsequent stages of development depending on the assigned priorities.
    07/2013;
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    ABSTRACT: Plasmons are quantized collective oscillations of electrons and have been observed in metals and doped semiconductors. The plasmons of ordinary, massive electrons have been the basic ingredients of research in plasmonics and in optical metamaterials for a long time. However, plasmons of massless Dirac electrons have only recently been observed in graphene, a purely two-dimensional electron system. Their properties are promising for novel tunable plasmonic metamaterials in the terahertz and mid-infrared frequency range. Dirac fermions also occur in the two-dimensional electron gas that forms at the surface of topological insulators as a result of the strong spin-orbit interaction existing in the insulating bulk phase. One may therefore look for their collective excitations using infrared spectroscopy. Here we report the first experimental evidence of plasmonic excitations in a topological insulator (Bi2Se3). The material was prepared in thin micro-ribbon arrays of different widths W and periods 2W to select suitable values of the plasmon wavevector k. The linewidth of the plasmon was found to remain nearly constant at temperatures between 6 K and 300 K, as expected when exciting topological carriers. Moreover, by changing W and measuring the plasmon frequency in the terahertz range versus k we show, without using any fitting parameter, that the dispersion curve agrees quantitatively with that predicted for Dirac plasmons.
    Nature Nanotechnology 07/2013; · 31.17 Impact Factor

Publication Stats

2k Citations
492.72 Total Impact Points

Institutions

  • 1989–2014
    • Sapienza University of Rome
      • Department of Physics
      Roma, Latium, Italy
  • 2013
    • INFN - Istituto Nazionale di Fisica Nucleare
      Frascati, Latium, Italy
  • 2010–2013
    • AREA Science Park
      Trst, Friuli Venezia Giulia, Italy
  • 2009–2013
    • Sincrotrone Trieste S.C.p.A.
      Trst, Friuli Venezia Giulia, Italy
  • 1994–1998
    • Université Paris-Sud 11
      Orsay, Île-de-France, France