Yazyev, O. V.
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.
Danailov, M. B.
De Monte, R.
De Ninno, G.
Di Mitri, S.
Fawley, W. 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.
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.
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.
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.
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.
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.
Bottrill, K. R. H.
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.
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.
Richardson, D. J.
Ellis, A. D.
Ben Ezra, S.
A regenerative optical grooming switch for interconnecting 100 Gbit/s networks with lower bit-rate networks and switching functionality in time, space and wavelength domain is demonstrated. Lab and field demonstrations show the feasibility of the new concept. Q-factors above 20 dB are reported.
Dal Conte, S.
van der Marel, D.
In strongly correlated materials the electronic and optical properties are significantly affected by the coupling of fermionic quasi particles to different degrees of freedom, such as lattice vibrations and bosonic excitations of electronic origin. Broadband ultrafast spectroscopy [1,2] is emerging as the premier technique to unravel the subtle interplay between quasi particles and electronic or phononic collective excitations, by their different characteristic timescales and spectral responses. By investigating the femtosecond dynamics of the optical properties of Bi2Sr2Ca0.92Y0.08Cu2O8+delta (Y-Bi2212) crystals over the 0.5-2 eV energy range, we disentangle the electronic and phononic contributions to the generalized electron-boson Eliashberg function [3,4], showing that the spectral distribution of the electronic excitations, such as spin fluctuations and current loops, and the strength of their interaction with quasi particles can account for the high critical temperature of the superconducting phase transition . Finally, we discuss how the use of this technique can be extended to the underdoped region of the phase diagram of cuprates, in which a pseudogap in the quasiparticle density of states opens. The microscopic modeling of the interaction of ultrashort light pulses with unconventional superconductors will be one of the key challenges of the next-years materials science, eventually leading to the full understanding of the role of the electronic correlations in controlling the dynamics on the femtosecond timescale.
The FERMI@Elettra free electron laser (FEL) user facility is currently under construction at the Sincrotrone Trieste laboratory in Trieste (Italy). It is a based on a seeded scheme that will provide an almost perfect transform limited beam and fully spatial coherent. It will cover the wavelength range from 100 to about 3 nm and in a short future down to 1 nm (by using higher harmonics). It is expected to be fully operative in the late summer of 2010. In this presentation we will report the layout of the photon beam diagnostics section with the preliminary tests, the radiation transport system to the experimental area, and the experimental hall facilities. A particular emphasis will be given to the optical solution and constrains due to the need of preserving the wave front and to avoid damage on the different optical elements, including slits, mirrors, gratings and all the diagnostic facilities. One of the main problems will be the necessity of using very large grazing incidence angle (up to 45 degrees) on multilayers and single coating mirrors. These elements are mandatory to perform the transient grating experiments and to realize the delay lines, where time delay up to 1 nsec are required. This issue poses a serious problem in terms of energy density delivered and adsorbed by the optics and great care must be taken into the choice of the proper multilayer materials. Some studies on the reflectivity of multilayers and Carbon coated mirrors will be reported as well as the diagnostic tools to monitor the quality of the optics in operative conditions.
Garg, K. B.
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.
Bottrill, K. R. H.
Richardson, D. J.
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.
Schoenlein, R. W.
Kieffer, J. C.
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.
Greaves, C. M. R.
Padmore, H. A.
dal Conte, S.
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.