We present the first observation of a prominent quasiparticle peak in the photoemission spectrum of the metallic phase of V2O3 and report new spectral calculations that combine the local-density approximation with the...
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We present the first observation of a prominent quasiparticle peak in the photoemission spectrum of the metallic phase of V2O3 and report new spectral calculations that combine the local-density approximation with the dynamical mean-field theory (using quantum Monte Carlo simulations) to show the development of such a distinct peak with decreasing temperature. The experimental peak width and weight are significantly larger than in the theory.
Femtosecond X-ray science is a new frontier in ultrafast research in which time-resolved measurement techniques are applied with X-ray pulses to investigate structural dynamics at the atomic scale on the fundamental t...
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We demonstrate a novel scheme for generating ultrashort pulses of synchrotron radiation. Our approach is to create femtosecond time-structure on a long electron bunch by using a femtosecond laser pulse to modulate the...
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We demonstrate a novel scheme for generating ultrashort pulses of synchrotron radiation. Our approach is to create femtosecond time-structure on a long electron bunch by using a femtosecond laser pulse to modulate the energy of an ultrashort slice of the bunch Femtosecond synchrotron pulses are directly measured from a bend-magnet beamline at the Advanced lightsource (ALS). The measured pulse duration is determined by the storage ring dispersion integrated from the wiggler to the radiation bend-magnet. A new beamline, dedicated to ultrafast X-ray spectroscopy is currently under construction at the ALS and will provide X-ray pulses of <100 fs duration. The femtosecond time structure is invariant over the entire spectral range of bend-magnet emission from the near infrared to the X-ray regime, making this a powerful tool for femtosecond X-ray spectroscopy.
We present the results of a systematic x-ray scattering study of the charge and orbital ordering in the manganite series Pr1−xCaxMnO3 with x=0.25, 0.4, and 0.5. The temperature dependence of the scattering at the char...
We present the results of a systematic x-ray scattering study of the charge and orbital ordering in the manganite series Pr1−xCaxMnO3 with x=0.25, 0.4, and 0.5. The temperature dependence of the scattering at the charge and orbital wavevectors, and of the lattice constants, was characterized throughout the ordered phase of each sample. It was found that the charge- and orbital-order wavevectors are commensurate with the lattice, in striking contrast to the results of electron and neutron diffraction studies of samples with x=0.5. High-momentum-transfer resolution studies of the x=0.4 and 0.5 samples further revealed that while long-range charge order is present, long-range orbital order is never established. Above the charge and orbital ordering temperature T0, the charge-order fluctuations are more highly correlated than the orbital fluctuations. This suggests that charge order drives orbital order in these samples. In addition, a longitudinal modulation of the lattice with the same periodicity as the charge and orbital ordering was discovered in the x=0.4 and 0.5 samples. For x=0.25, only long-range orbital order was observed with no indication of charge ordering, nor of an additional lattice modulation. We also report the results of a preliminary investigation of the loss of charge and orbital ordering in the x=0.4 sample by application of a magnetic field. Finally, the polarization and azimuthal dependence of the charge and orbital ordering in these compounds are characterized both in the resonant and nonresonant limits, and compared with the predictions of current theories. The results are qualitatively consistent with both cluster and local density approximation +U calculations of the electronic structure.
Although x-ray micro-foci can be produced by a variety of diffractive methods, grazing incidence mirrors are the only route to an achromatic focus. In this paper we describe our efforts to produce elliptically shaped ...
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ISBN:
(纸本)0819422444
Although x-ray micro-foci can be produced by a variety of diffractive methods, grazing incidence mirrors are the only route to an achromatic focus. In this paper we describe our efforts to produce elliptically shaped mirrors with the very high figure accuracy necessary for producing a micro-focus. The motivation for this work is provided by the need to produce achromatic foci for a range of applications ranging from tunable micro-focus x-ray photoelectron spectroscopy (mu-XPS) at soft x-ray energies to micro-focus white beam x-ray diffraction (mu-XRD) at hard x-ray energies. We describe the methodology of beam bending, a practical example of a system we have produced for mu-XRD, and results demonstrating the production of a surface with micro-radian figure accuracy.
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