Light-enhanced Charge Density Wave Coherence in a High-Temperature Superconductor

In high-T$_{C}$ cuprates, superconductivity and charge density waves (CDW) are competitive, yet coexisting orders. To understand their microscopic interdependence a probe capable of discerning their interaction on its natural length and time scales is necessary. Here we use ultrafast resonant soft x-ray scattering to track the transient evolution of CDW correlations in YBa$_{2}$Cu$_{3}$O$_{6+x}$ following the quench of superconductivity by an infrared laser pulse. We observe a picosecond non-thermal response of the CDW order, characterized by a large enhancement of spatial coherence, nearly doubling the CDW correlation length, while only marginally affecting its amplitude. This ultrafast snapshot of the interaction between order parameters demonstrates that their competition manifests inhomogeneously through disruption of spatial coherence, and indicates the role of superconductivity in stabilizing topological defects within CDW domains.Comment: 29 pages, 9 figures, Main text and Supplementary Material

Enhanced charge density wave coherence in a light-quenched, high-temperature superconductor

Superconductivity and charge density waves (CDWs) are competitive, yet coexisting, orders in cuprate superconductors. To understand their microscopic interdependence, a probe capable of discerning their interaction on its natural length and time scale is necessary. We use ultrafast resonant soft x-ray scattering to track the transient evolution of CDW correlations in YBa2Cu3O6+x after the quench of superconductivity by an infrared laser pulse. We observe a nonthermal response of the CDW order characterized by a near doubling of the correlation length within ≈1 picosecond of the superconducting quench. Our results are consistent with a model in which the interaction between superconductivity and CDWs manifests inhomogeneously through disruption of spatial coherence, with superconductivity playing the dominant role in stabilizing CDW topological defects, such as discommensurations

Coherence properties of focused X-ray beams at high-brilliance synchrotron sources

An analytical approach describing properties of focused partially coherent X-ray beams is presented. The method is based on the results of statistical optics and gives both the beam size and transverse coherence length at any distance behind an optical element. In particular, here Gaussian Schell-model beams and thin optical elements are considered. Limiting cases of incoherent and fully coherent illumination of the focusing element are discussed. The effect of the beam-defining aperture, typically used in combination with focusing elements at synchrotron sources to improve transverse coherence, is also analyzed in detail. As an example, the coherence properties in the focal region of compound refractive lenses at the PETRA III synchrotron source are analyzed

PERSPECTIVAS DEL PROCESO DE GLOBALIZACIÓN Y SU INFLUENCIA SOBRE LOS DERECHOS HUMANOS ECONÓMICOS, SOCIALES Y CULTURALES

El escenario internacional se encuentra en constante transformación debido a lo que se ha denominado el proceso de “globalización”. Este afecta las relaciones internaciones interestatales e influye en la vida cotidiana de los individuos. El Derecho Internacional y más específicamente el Derecho Internacional de los Derechos Humanos no es ajeno a este proceso. La investigación afirma que nos encontramos frente a una etapa de transnacionalización de los Derechos Humanos, que permite que los individuos cuenten con mayor protección en ámbitos supranacionales. También hace especial mención a los derechos Económicos Sociales y Culturales, analiza el debate sobre el pluralismo jurídico y la eficacia diferencial. En la metodología empleada se revisan fuentes documentales y se realiza un análisis de algunos derechos particulares previstos en el Pacto de Derechos Económicos, Sociales y Culturales. Los planteamientos permiten afirmar que el proceso de globalización ha determinado la transnacionalización de los Derechos Humanos, surgiendo de dicho fenómeno consecuencias positivas y negativas en cuanto a su cumplimiento

Digital Orbit Feedback Compensation For Spear *

The global orbit feedback system for SPEAR will be upgraded in 1995 to achieve 30-50Hz closed loop bandwidth. In this paper, we discuss issues related to measurements of the corrector frequency response, the DC response matrix, digital compensator design, and the impact of sequential bpm sampling. Results from detailed simulations are included. 1. INTRODUCTION SPEAR is a 234m synchrotron light source that was originally designed for e - - e + collider physics. Because of this history, many features built into 3 rd generation light sources are not available in SPEAR. The bpms, for instance, were installed before the modern notions of accelerator impedance were developed, and their geometry was not optimized for high resolution measurements. In addition, many of the magnets are subject to thermal fluctuations, hysteresis, and to ground motion propagating through girder supports. These vibrations lead to electron beam motion in the 1-20Hz range, and diurnal drift of the orbit. At..

Quadrupole Shunt Experiments at SPEAR*

Abstract. As part of a program to align and stabilize the SPEAR storage ring, a switchable shunt resistor was installed on each quadrupole to bypass a small percentage of the magnet current. The impact of a quadrupole shunt is to move the electron beam orbit in proportion to the off-axis beam position at the quadrupole and to shift the betatron tune. Initially, quadrupole shunts in SPEAR were used to position the electron beam in the center of the quadrupoles This provided readback offsets for nearby beam position monitors, and helped to steer the photon beams with low-amplitude corrector currents. The shunt-induced tune shift measurements were then processed in MAD to derive a lattice model

Investigation of Beam Alignment Monitor Technologies for the LCLS FEL Undulator?

Abstract. To maintain gain in the proposed 100 m long linac-driven Linac Coherent Light Source (LCLS) Free Electron Laser (FEL) undulator, the electron and photon beams must propagate colinearly to within-5 urn rms over distances comparable to the 11.7 m FEL gain length in the 6 mm diameter undulator vacuum chamber. We have considered a variety of intercepting and non-intercepting position monitor technologies to establish and maintain this beam alignment. We present a summary discussion of the applicability and estimated performance of monitors detecting synchrotron radiation, transition and diffraction radiation, fluorescence, photoemission or bremsstrahlung from thin wires, Compton scattering from laser beams, and image currents from the electron beam. We conclude that: 1) non-intercepting rf cavity electron BPMs, together with a beam-based alignment system, are best suited for this application; and 2) insertable, intercepting wire monitors are valuable for rough alignment, for beam size measurements, and for simultaneous measurement of electron and photon beam position by detecting bremsstrahlung from electrons and diffracted x-rays from the photon heam