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Now showing items 1 - 16 of 88

  • Temperature dependent non-monotonic bands shift in ZrTe5

    Manzoni, G.   Crepaldi, A.   Autes, G.   Sterzi, A.   Cilento, F.   Akrap, A.   Vobornik, I.   Gragnaniello, L.   Bugnon, Ph.   Fonin, M.   Berger, H.   Zacchigna, M.   Yazyev, O. V.   Parmigiani, F.  

    The electronic structure of ZrTe5 has been matter of renewed interest aimed at clarifying, along with its topological character, the temperature dependence of the unusual transport properties of this material. Here, we report an extensive high resolution Angle Resolved Photoelectron Spectroscopy (ARPES) study unveiling a non-monotonic shift of the bands, when the sample temperature is varied between 16K and 300K. Moreover, the present conventional ARPES and circularly dichroic ARPES measurements reveal the presence of two states at the top of the valence band. The strong ARPES dichroic signal detected in proximity of the Fermi energy has been interpreted as the indication of the presence of spin polarized states, in agreement with the predicted strong topological character of this material. (c) 2016 Elsevier B.V. All rights reserved.
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  • The FERMI free-electron lasers

    Allaria, E.   Badano, L.   Bassanese, S.   Capotondi, F.   Castronovo, D.   Cinquegrana, P.   Danailov, M. B.   D'Auria, G.   Demidovich, A.   De Monte, R.   De Ninno, G.   Di Mitri, S.   Diviacco, B.   Fawley, W. M.   Ferianis, M.   Ferrari, E.   Gaio, G.   Gauthier, D.   Giannessi, L.   Iazzourene, F.   Kurdi, G.   Mahne, N.   Nikolov, I.   Parmigiani, F.   Penco, G.   Raimondi, L.   Rebernik, P.   Rossi, F.   Roussel, E.   Scafuri, C.   Serpico, C.   Sigalotti, P.   Spezzani, C.   Svandrlik, M.   Svetina, C.   Trovo, M.   Veronese, M.   Zangrando, D.   Zangrando, M.  

    FERMI is a seeded free-electron laser (FEL) facility located at the Elettra laboratory in Trieste, Italy, and is now in user operation with its first FEL line, FEL-1, covering the wavelength range between 100 and 20 nm. The second FEL line, FEL-2, a high-gain harmonic generation double-stage cascade covering the wavelength range 20-4 nm, has also completed commissioning and the first user call has been recently opened. An overview of the typical operating modes of the facility is presented.
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  • MagneDyn: the future beamline for ultrafast magnetodynamical studies at FERMI

    Svetina, C.   Dell'Angela, M.   Mahne, N.   Malvestuto, M.   Parmigiani, F.   Raimondi, L.   Zangrando, M.  

    The future beamline Magneto Dynamics (MagneDyn) will be devoted to study the electronic states and the local magnetic properties of excited and transient states of complex systems by means of the time-resolved X-ray absorption spectroscopy (TR-XAS) technique. The beamline will use the high energy source at FERMI covering the wavelength range from 60 nm down to 1.3 nm. An on-line photon energy spectrometer will allow to measure the spectrum with high resolution while delivering most of the beam to the end-stations. Downstream the beam will be possibly split and delayed, by means of a delay line, and then focused with a set of active KB mirrors. These mirrors will be able to focus the radiation in one of the two MagneDyn experimental chambers: the electro-magnet end-station and the Resonant Inelastic X-ray Scattering (RIXS) end-station. After an introduction of MagneDyn scientific case, we will discuss the layout showing the expected performances of the beamline.
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  • Arterio-venous malformation of the mandible. Case report and review of literature

    Spreafico, R.   Sordo, L.   Bellotto, R.   Schipano, M.   Rescaldani, A.   Parmigiani, F.  

    Arteriovenous malformation (AVM) of the head and neck is a rare and potentially life threatening entity due to massive haemorrhage. There are several indications for treatment, including age of the patient and location, extent and type of vascular malformation. Endovascular therapy can effectively cure most lesions with limited tissue involvement. Surgery can be used in selected cases in combination with embolization. Here we report the case of a young woman affected by a massive AVM on the left side of the mandible and submandibular region, and also review the literature on AVM with special attention to treatment strategies.
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  • Phase sensitive amplification in a highly nonlinear lead-silicate fiber

    Ettabib, M.A.   Jones, L.   Kakande, J.   Slavi'k, R.   Parmigiani, F.   Xian Feng   Poletti, F.   Ponzo, G.M.   Jindan Shi   Petrovich, M.N.   Loh, W.H.   Petropoulos, P.   Richardson, D.J.  

    We experimentally demonstrate phase-sensitive amplification in a highly nonlinear and low-dispersion lead-silicate W-type fiber. A phase-sensitive gain variation of 6 dB was observed in a 1.56-m sample of the fiber for a total input pump power of 27.7 dBm.
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  • Progress in Multichannel All-Optical Regeneration Based on Fiber Technology

    Parmigiani, F.   Provost, L.   Petropoulos, P.   Richardson, D.J.   Freude, W.   Leuthold, J.   Ellis, A.D.   Tomkos, I.  

    Multiwavelength all-optical regeneration has the potential to substantially increase both the capacity and scalability of future optical networks. In this paper, we review recent promising developments in this area. First, we recall the basic principles of multichannel regeneration of high bit rate signals in optical communication systems before discussing the current technological approaches. We then describe in detail two fiber-based multichannel 2R regeneration techniques for return-to-zero-on-off keying based on 1) dispersion managed systems and 2) direction and polarization multiplexing. We present results illustrating the levels of performance so far achieved and discuss various practical issues and prospects for further performance enhancement.
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  • Ferromagnetism in graphene-Mn(x)Si(1-x) heterostructures grown on 6H-SiC(0001)

    Magnano, E.   Bondino, F.   Cepek, C.   Sangaletti, L.   Mozzati, M.C.   Parmigiani, F.  

    The fabrication of Mn-doped SiC materials by thermal reaction is an interesting method for obtaining SiC-based ferromagnetic semiconductors. Here we used x-ray photoemission and absorption measurements to study the reaction and diffusion of Mn in a 6 H-SiC single crystal substrate induced by a thermal treatment. In particular we have detected the formation of Mn-Si alloys completely covered by a graphene layer. The temperature dependence of the magnetization curves reveals the presence of two distinct magnetic phases. Interestingly, one of these phases displays ferromagnetic character at temperatures close to room temperature.
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  • Phase Regeneration of QPSK Signal in SOA Using Single-Stage,Wavelength Converting PSA

    Bottrill, K. R. H.   Kakarla, R.   Parmigiani, F.   Venkitesh, D.   Petropoulos, P.  

    We demonstrate, for the first time, all-optical phase regeneration of a quaternary phase shift keying signal through phase sensitive amplification in nonlinear semiconductor optical amplifiers (SOAs), using a scheme only previously demonstrated in highly nonlinear fibre. We make use of a highly tunable phase quantizing scheme to circumvent some of the limitations imposed by the use of SOAs and show that it may function in either a conjugating or nonconjugating manner.
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  • The FERMI@Elettra FEL Photon Transport System

    Zangrando, M.   Cudin, I.   Fava, C.   Godnig, R.   Kiskinova, M.   Masciovecchio, C.   Parmigiani, F.   Rumiz, L.   Svetina, C.   Turchet, A.   Cocco, D.  

    The FERMI@Elettra free electron laser (FEL) user facility is under construction at Sincrotrone Trieste (Italy), and it will be operative in late 2010. It is based on a seeded scheme providing an almost perfect transform-limited and fully spatially coherent photon beam. FERMI@Elettra will cover the wavelength range 100 to 3 nm with the fundamental harmonics, and down to 1 nm with higher harmonics. We present the layout of the photon beam transport system that includes: the first common part providing on-line and shot-to-shot beam diagnostics, called PADReS (Photon Analysis Delivery and Reduction System), and 3 independent beamlines feeding the experimental stations. Particular emphasis is given to the solutions adopted to preserve the wavefront, and to avoid damage on the different optical elements. Peculiar FEL devices, not common in the Synchrotron Radiation facilities, are described in more detail, e.g. the online photon energy spectrometer measuring shot-by-shot the spectrum of the emitted radiation, the beam splitting and delay line system dedicated to cross/auto correlation and pump-probe experiments, and the wavefront preserving active optics adapting the shape and size of the focused spot to meet the needs of the different experiments.
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  • Study of Sb substitution for Pr in the Pr(0.67)Ba(0.33)MnO(3) system

    Garg, K. B.   Nordblad, P.   Heinonen, M.   Panwar, N.   Sen, V.   Bondino, F.   Magnano, E.   Carleschi, E.   Parmigiani, F.   Agarwal, S. K.  

    We study the effect of Sb substitution for Pr in the hole-doped system Pr(0.67)Ba(0.33)MnO(3) (PBMO) for different doping levels of Sb. The two electrical resistivity transitions observed in the pristine sample PBMO shift to low temperatures on Sb doping with an overall increase in the electrical resistivity. The significant local lattice distortion and the grain boundary effects caused by the large cation size mismatch between Pr(3+) and Sb(3+) suppresses the double-exchange (DE) interaction and enhances the super-exchange (SE) interaction. The compounds show a significant and increasing value of magnetoresistance at temperatures below the Curie temperature, not expected from the DE model. The Curie temperature decreases with increase in Sb content but the saturation magnetization is little affected by the substitution. The spins, however, stay well aligned in the low-temperature regime. Our X-ray near-edge absorption spectra (XANES) and core level photoemission (XPS) data clearly show the Sb cation to be in +3 state and rule out any possibility of e-doping in our compounds. (C) 2008 Elsevier B. V. All rights reserved.
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  • Multi-Channel Phase Regenerator Based on Polarization-Assisted Phase-Sensitive Amplification

    Parmigiani, F.   Bottrill, K. R. H.   Slavik, R.   Richardson, D. J.   Petropoulos, P.  

    We propose and demonstrate simultaneous phase regeneration of six nonreturn-to-zero binary phase shift keying signals in a single nonlinear medium. The regenerating system, which exhibits binary steplike phase transfer functions, uses four-wave mixing in degenerate dual-pump vector parametric amplifiers implemented in the same nonlinear optical fiber, followed by polarization filtering. Bit-error-ratio measurements confirm optical-signal-to-ratio improvement and negligible crosstalk across all the regenerated channels, which were impaired at the regenerator input by broadband phase noise.
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  • Optical switching in VO(2) films by below-gap excitation

    Rini, M.   Hao, Z.   Schoenlein, R. W.   Giannetti, C.   Parmigiani, F.   Fourmaux, S.   Kieffer, J. C.   Fujimori, A.   Onoda, M.   Wall, S.   Cavalleri, A.  

    We study the photoinduced insulator-metal transition in VO(2), correlating its threshold and dynamics with excitation wavelength. In single crystals, switching can only be induced with photon energies above the 670 meV gap. This contrasts,with the case of polycrystalline films, where formation of the metallic state can be initiated also with photon energies as low as 180 meV, which are well below the bandgap. Perfection of this process may become conducive to schemes for optical switches, limiters, and detectors operating at room temperature in the mid-infrared. (C) 2008 American Institute of Physics.
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  • Surface and bulk contribution to Cu(111) quantum efficiency RID G-2395-2010

    Pedersoli, E.   Greaves, C. M. R.   Wan, W.   Coleman-Smith, C.   Padmore, H. A.   Pagliara, S.   Cartella, A.   Lamarca, F.   Ferrini, G.   Galimberti, G.   Montagnese, M.   dal Conte, S.   Parmigiani, F.  

    The quantum efficiency (QE) of Cu(111) is measured for different impinging light angles with photon energies just above the work function. We observe that the vectorial photoelectric effect, an enhancement of the QE due to illumination with light with an electric vector perpendicular to the sample surface, is stronger in the more surface sensitive regime. This can be explained by a contribution to photoemission due to the variation in the electromagnetic potential at the surface. The contributions of bulk and surface electrons can then be determined.
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  • Time-division-multiplexing using pulse position locking for 100 Gb/s applications

    Chow, C. W.   Ellis, A. D.   Parmigiani, F.  

    Recently, there is a great interest in pushing communication technologies to 100 Gb/s. However, there are still many challenges to perform high speed (> 40 Gb/s) clock and data recovery, and data time-division-multiplexing (TDM). Here, we propose and numerically analyze an asynchronous optical packet retimer using parabolic or sinusoidal phase modulation and linear dispersion. This scheme is named pulse position locking (PPL). Numerical simulation shows that this scheme can effectively resynchronize input signals with arbitrary delays to the local clock, and reduce input jitter. The scheme can also be applied to TDM 10 Gb/s and 40 Gb/s signals to over 100 Gb/s. (C) 2009 Optical Society of America
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  • Time domain add-drop multiplexing scheme enhanced using a saw-tooth pulse shaper

    Parmigiani, F.   Petropoulos, P.   Ibsen, M.   Almeida, P.J.   Ng, T.T.   Richardson, D.J.  

    We experimentally demonstrate the use of saw-tooth optical pulses, which are shaped using a fiber Bragg grating, to achieve robust and high performance time-domain add-drop multiplexing in a scheme based on cross-phase (XPM) modulation in an optical fiber, with subsequent offset filtering. As compared to the use of more conventional pulse shapes, such as Gaussian pulses of a similar pulse width, the purpose-shaped saw-tooth pulses allow higher extinction ratios for the add and drop windows and significant improvements in the receiver sensitivity for the dropped and added channels.
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  • Time domain add–drop multiplexing scheme enhanced using a saw-tooth pulse shaper

    Parmigiani, F.   Petropoulos, P.   Ibsen, M.   Almeida, P. J.   Ng, T. T.   Richardson, D. J.  

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