Quenched lattice fluctuations in optically driven SrTiO3.

Crystal lattice fluctuations, which are known to influence phase transitions of quantum materials in equilibrium, are also expected to determine the dynamics of light-induced phase changes. However, they have only rarely been explored in these dynamical settings. Here we study the time evolution of lattice fluctuations in the quantum paraelectric SrTiO3, in which mid-infrared drives have been shown to induce a metastable ferroelectric state. Crucial in these physics is the competition between polar instabilities and antiferrodistortive rotations, which in equilibrium frustrate the formation of long-range ferroelectricity. We make use of high-intensity mid-infrared optical pulses to resonantly drive the Ti-O-stretching mode at 17 THz, and we measure the resulting change in lattice fluctuations using time-resolved X-ray diffuse scattering at a free-electron laser. After a prompt increase, we observe a long-lived quench in R-point antiferrodistortive lattice fluctuations. Their enhancement and reduction are theoretically explained by considering the fourth-order nonlinear phononic interactions to the driven optical phonon and third-order coupling to lattice strain, respectively. These observations provide a number of testable hypotheses for the physics of light-induced ferroelectricity.

The ultrafast Einstein-de Haas effect.

The Einstein-de Haas effect was originally observed in a landmark experiment1 demonstrating that the angular momentum associated with aligned electron spins in a ferromagnet can be converted to mechanical angular momentum by reversing the direction of magnetization using an external magnetic field. A related problem concerns the timescale of this angular momentum transfer. Experiments have established that intense photoexcitation in several metallic ferromagnets leads to a drop in magnetization on a timescale shorter than 100 femtoseconds-a phenomenon called ultrafast demagnetization2-4. Although the microscopic mechanism for this process has been hotly debated, the key question of where the angular momentum goes on these femtosecond timescales remains unanswered. Here we use femtosecond time-resolved X-ray diffraction to show that most of the angular momentum lost from the spin system upon laser-induced demagnetization of ferromagnetic iron is transferred to the lattice on sub-picosecond timescales, launching a transverse strain wave that propagates from the surface into the bulk. By fitting a simple model of the X-ray data to simulations and optical data, we estimate that the angular momentum transfer occurs on a timescale of 200 femtoseconds and corresponds to 80 per cent of the angular momentum that is lost from the spin system. Our results show that interaction with the lattice has an essential role in the process of ultrafast demagnetization in this system.

Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa2Cu3O6.5.

Terahertz-frequency optical pulses can resonantly drive selected vibrational modes in solids and deform their crystal structures. In complex oxides, this method has been used to melt electronic order, drive insulator-to-metal transitions and induce superconductivity. Strikingly, coherent interlayer transport strongly reminiscent of superconductivity can be transiently induced up to room temperature (300 kelvin) in YBa2Cu3O6+x (refs 9, 10). Here we report the crystal structure of this exotic non-equilibrium state, determined by femtosecond X-ray diffraction and ab initio density functional theory calculations. We find that nonlinear lattice excitation in normal-state YBa2Cu3O6+x at above the transition temperature of 52 kelvin causes a simultaneous increase and decrease in the Cu-O2 intra-bilayer and, respectively, inter-bilayer distances, accompanied by anisotropic changes in the in-plane O-Cu-O bond buckling. Density functional theory calculations indicate that these motions cause drastic changes in the electronic structure. Among these, the enhancement in the character of the in-plane electronic structure is likely to favour superconductivity.

Towards X-ray transient grating spectroscopy.

The extension of transient grating spectroscopy to the x-ray regime will create numerous opportunities, ranging from the study of thermal transport in the ballistic regime to charge, spin, and energy transfer processes with atomic spatial and femtosecond temporal resolution. Studies involving complicated split-and-delay lines have not yet been successful in achieving this goal. Here we propose a novel, simple method based on the Talbot effect for converging beams, which can easily be implemented at current x-ray free electron lasers. We validate our proposal by analyzing printed interference patterns on polymethyl methacrylate and gold samples using ∼3 keV X-ray pulses.

Spatial Distortion of Vibration Modes via Magnetic Correlation of Impurities.

Long wavelength vibrational modes in the ferromagnetic semiconductor Ga_{0.91}Mn_{0.09}As are investigated using time resolved x-ray diffraction. At room temperature, we measure oscillations in the x-ray diffraction intensity corresponding to coherent vibrational modes with well-defined wavelengths. When the correlation of magnetic impurities sets in, we observe the transition of the lattice into a disordered state that does not support coherent modes at large wavelengths. Our measurements point toward a magnetically induced broadening of long wavelength vibrational modes in momentum space and their quasilocalization in the real space. More specifically, long wavelength vibrational modes cannot be assigned to a single wavelength but rather should be represented as a superposition of plane waves with different wavelengths. Our findings have strong implications for the phonon-related processes, especially carrier-phonon and phonon-phonon scattering, which govern the electrical conductivity and thermal management of semiconductor-based devices.

X-ray and optical wave mixing.

Light-matter interactions are ubiquitous, and underpin a wide range of basic research fields and applied technologies. Although optical interactions have been intensively studied, their microscopic details are often poorly understood and have so far not been directly measurable. X-ray and optical wave mixing was proposed nearly half a century ago as an atomic-scale probe of optical interactions but has not yet been observed owing to a lack of sufficiently intense X-ray sources. Here we use an X-ray laser to demonstrate X-ray and optical sum-frequency generation. The underlying nonlinearity is a reciprocal-space probe of the optically induced charges and associated microscopic fields that arise in an illuminated material. To within the experimental errors, the measured efficiency is consistent with first-principles calculations of microscopic optical polarization in diamond. The ability to probe optical interactions on the atomic scale offers new opportunities in both basic and applied areas of science.

[Nationwide implementation of a hospital resource register for daily trauma care, mass casualties and disasters : Position paper of the German Trauma Society and the Federation of German Medical Directors of Emergency Medical Services]. / Bundesweite Einführung eines Krankenhauskatasters in den Klinikalltag und bei Großschadens- und Bedrohungslagen : Positionspapier der DGU und des BV-ÄLRD e. V.

The introduction of requirements for a minimum intake capacity of trauma patients by the German Trauma Society (DGU) into the so-called white book of treatment of seriously injured patients, is helpful for a sufficient preparation for threats and for dealing with mass casualties for trauma centers as well as for the emergency medical services (EMS). In the hospital information database provided by the Federation of German Medical Directors of Emergency Medical Services, more than 1300 hospitals are currently listed. This information supports the allocation of trauma patients from the field to the appropriate trauma center. Currently, without any coordination requirements, the current 626 trauma centers in Germany are able to immediately handle 6260 patients. This number could be doubled by activating the local hospital action plan, where a priority plan is set up. Additionally, the implementation of a nationwide flexible standardized communication structure between the dispatch center of the ambulance service and the hospitals, would improve daily care as well as the management of threats and mass casualties. It is the obligation of the local medical director of the EMS, to maintain and update the hospital database. Providing the information in the database with the hospital resources and the flexible standard communication structure, is appropriate to improve the daily collaboration and the preparation for mass casualties.

Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr2IrO4.

Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity. Recently, photo-excitation has been used to induce similarly exotic states transiently. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. The marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.

Nonlinear Electron-Phonon Coupling in Doped Manganites.

We employ time-resolved resonant x-ray diffraction to study the melting of charge order and the associated insulator-to-metal transition in the doped manganite Pr_{0.5}Ca_{0.5}MnO_{3} after resonant excitation of a high-frequency infrared-active lattice mode. We find that the charge order reduces promptly and highly nonlinearly as function of excitation fluence. Density-functional theory calculations suggest that direct anharmonic coupling between the excited lattice mode and the electronic structure drives these dynamics, highlighting a new avenue of nonlinear phonon control.

Multiple Supersonic Phase Fronts Launched at a Complex-Oxide Heterointerface.

Selective optical excitation of a substrate lattice can drive phase changes across heterointerfaces. This phenomenon is a nonequilibrium analogue of static strain control in heterostructures and may lead to new applications in optically controlled phase change devices. Here, we make use of time-resolved nonresonant and resonant x-ray diffraction to clarify the underlying physics and to separate different microscopic degrees of freedom in space and time. We measure the dynamics of the lattice and that of the charge disproportionation in NdNiO_{3}, when an insulator-metal transition is driven by coherent lattice distortions in the LaAlO_{3} substrate. We find that charge redistribution propagates at supersonic speeds from the interface into the NdNiO_{3} film, followed by a sonic lattice wave. When combined with measurements of magnetic disordering and of the metal-insulator transition, these results establish a hierarchy of events for ultrafast control at complex-oxide heterointerfaces.

Photoinduced Enhancement of the Charge Density Wave Amplitude.

Symmetry breaking and the emergence of order is one of the most fascinating phenomena in condensed matter physics. It leads to a plethora of intriguing ground states found in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting states of matter far from equilibrium can provide even more striking routes to symmetry-lowered, ordered states. Here, we demonstrate for the case of elemental chromium that moderate ultrafast photoexcitation can transiently enhance the charge-density-wave (CDW) amplitude by up to 30% above its equilibrium value, while strong excitations lead to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interactions, providing an efficient mechanism to selectively transform a broad excitation of the electronic order into a well-defined, long-lived coherent lattice vibration. This mechanism may be exploited to transiently enhance order parameters in other systems with coupled degrees of freedom.

Demonstration of simultaneous experiments using thin crystal multiplexing at the Linac Coherent Light Source.

Multiplexing of the Linac Coherent Light Source beam was demonstrated for hard X-rays by spectral division using a near-perfect diamond thin-crystal monochromator operating in the Bragg geometry. The wavefront and coherence properties of both the reflected and transmitted beams were well preserved, thus allowing simultaneous measurements at two separate instruments. In this report, the structure determination of a prototypical protein was performed using serial femtosecond crystallography simultaneously with a femtosecond time-resolved XANES studies of photoexcited spin transition dynamics in an iron spin-crossover system. The results of both experiments using the multiplexed beams are similar to those obtained separately, using a dedicated beam, with no significant differences in quality.

A time-dependent order parameter for ultrafast photoinduced phase transitions.

Strongly correlated electron systems often exhibit very strong interactions between structural and electronic degrees of freedom that lead to complex and interesting phase diagrams. For technological applications of these materials it is important to learn how to drive transitions from one phase to another. A key question here is the ultimate speed of such phase transitions, and to understand how a phase transition evolves in the time domain. Here we apply time-resolved X-ray diffraction to directly measure the changes in long-range order during ultrafast melting of the charge and orbitally ordered phase in a perovskite manganite. We find that although the actual change in crystal symmetry associated with this transition occurs over different timescales characteristic of the many electronic and vibrational coordinates of the system, the dynamics of the phase transformation can be well described using a single time-dependent 'order parameter' that depends exclusively on the electronic excitation.

Imaging Molecular Motion: Femtosecond X-Ray Scattering of an Electrocyclic Chemical Reaction.

Structural rearrangements within single molecules occur on ultrafast time scales. Many aspects of molecular dynamics, such as the energy flow through excited states, have been studied using spectroscopic techniques, yet the goal to watch molecules evolve their geometrical structure in real time remains challenging. By mapping nuclear motions using femtosecond x-ray pulses, we have created real-space representations of the evolving dynamics during a well-known chemical reaction and show a series of time-sorted structural snapshots produced by ultrafast time-resolved hard x-ray scattering. A computational analysis optimally matches the series of scattering patterns produced by the x rays to a multitude of potential reaction paths. In so doing, we have made a critical step toward the goal of viewing chemical reactions on femtosecond time scales, opening a new direction in studies of ultrafast chemical reactions in the gas phase.

Impaired brachial artery endothelial function in young healthy women following an acute painful stimulus.

INTRODUCTION: Impaired endothelial function has been observed during and immediately following an acutely painful stimulus. However, the extent to which this persists following pain dissipation is unclear. PURPOSE: To determine whether painful ischemic handgrip exercise (pain task) causes impaired flow-mediated dilation (FMD) after the sensation of pain and hemodynamic responses have abated. A second purpose was to determine whether the response to pain differed with a predisposition to magnify, ruminate, and feel helpless about pain (pain catastrophizing status). METHODS: Brachial artery FMD stimulated by reactive hyperemia was assessed via ultrasound in 18 (9 high catastrophizing) healthy, women (20 ± 1 years) before and 15 min after a 3 min pain task. The shear stress stimulus for FMD was estimated as shear rate (blood velocity/brachial artery diameter). RESULTS (MEAN ± SD): None of the variables were significantly impacted by pain catastrophizing status and are presented pooled across group. The pain task increased pain ratings [1 ± 1-6 ± 3 (0-10 scale) (p < 0.001)], mean arterial pressure (MAP) (p < 0.001) and heart rate (HR) (p < 0.001), all returning to pre-pain levels ≤2-min post-pain task (pre-pain vs. 2-min post-pain: pain rating p = 1.000; MAP p = 0.142; HR p = 0.992). The shear rate stimulus was not different between pre- and post-pain task FMD tests (p = 0.200). FMD decreased post-pain task (10.8 ± 4.6 vs. 7.0 ± 2.7 %, p < 0.001). CONCLUSION: These results indicate that, regardless of pain catastrophizing status, painful ischemic handgrip exercise has a deleterious impact on endothelial function that persists after the pain sensation and hemodynamic responses have abated.

Demonstration of single-crystal self-seeded two-color x-ray free-electron lasers.

A scheme for generating two simultaneous hard-x-ray free-electron laser pulses with a controllable difference in photon energy is described and then demonstrated using the self-seeding setup at the Linac Coherent Light Source (LCLS). The scheme takes advantage of the existing LCLS equipment, which allows two independent rotations of the self-seeding diamond crystal. The two degrees of freedom are used to select two nearby crystal reflections, causing two wavelengths to be present in the forward transmitted seeding x-ray pulse. The free-electron laser system must support amplification at both desired wavelengths.

Immediate Unprotected Weightbearing vs 2 Weeks Nonweightbearing After Open Reduction Internal Fixation of Ankle Fractures.

BACKGROUND: Postoperative care protocols for ankle fracture surgery remain controversial with variability among care providers. This prospective controlled trial compared 12-week postoperative outcomes for immediate unprotected weightbearing (IMWB) vs nonweightbearing (NWB) for 2 weeks in a splint followed by weightbearing as tolerated (WBAT) in a boot after surgical fixation of selected low-energy ankle fractures without superior articular involvement. METHODS: Eighty-seven patients undergoing surgical fixation of ankle fractures at a single level 1 trauma center were recruited according to specific criteria and enrolled by presentation date. The first 43 eligible patients were allocated to the control group, with NWB in a splint for 2 weeks followed by WBAT in a walker boot. The next 44 patients recruited were allocated to the IMWB group. The primary outcome was the Olerud-Molander score (OMAS). Secondary outcome measures included the Euroquol-5D (EQ5D) score and Work Productivity and Activity Impairment: Specific Health Problem (WPAI:SHP) scores, ankle range of motion (ROM), wound complications, time to return to work, radiograph measurements, and fracture reduction loss. In this perioperative-focused study, we collected data on patients until 12 weeks postoperation. RESULTS: The IMWB group had 5 superficial wound complications vs 1 in the control group. At 12 weeks, we found no difference in OMAS, EQ5D, WPAI:SHP scores, ROM, time to return to work, or radiographic measurements. CONCLUSION: In this short-term and relatively small prospective trial, we found more wound complications among patients treated with immediate unprotected weightbearing compared with patients treated with 2 weeks of NWB followed by protected weightbearing. Given the low incidence and small sample size, we do not know if these observed findings are generalizable. However, we also found no difference in functional outcomes at 12 weeks postoperation between these 2 groups. In light of that, we do not recommend IMWB after open reduction internal fixation of low-energy ankle fractures with plate and/or screw fixation. LEVEL OF EVIDENCE: Level II, prospective controlled trial.

Single shot speckle and coherence analysis of the hard X-ray free electron laser LCLS.

The single shot based coherence properties of hard x-ray pulses from the Linac Coherent Light Source (LCLS) were measured by analyzing coherent diffraction patterns from nano-particles and gold nanopowder. The intensity histogram of the small angle x-ray scattering ring from nano-particles reveals the fully transversely coherent nature of the LCLS beam with a number of transverse mode 〈Ms〉 = 1.1. On the other hand, the speckle contrasts measured at a large wavevector yields information about the longitudinal coherence of the LCLS radiation after a silicon (111) monochromator. The quantitative agreement between our data and the simulation confirms a mean coherence time of 2.2 fs and a x-ray pulse duration of 29 fs. Finally the observed reduction of the speckle contrast generated by x-rays with pulse duration longer than 30 fs indicates ultrafast dynamics taking place at an atomic length scale prior to the permanent sample damage.

FGF23 is independently associated with vascular calcification but not bone mineral density in patients at various CKD stages.

SUMMARY: The hormone fibroblast growth factor 23 (FGF23) is involved in mineral homeostasis but may also have a role in vascular calcification and bone mineralization. In a cohort of 142 patients with CKD stages 2-5D, plasma FGF23 was independently associated with aortic calcification but not with pulse wave velocity or bone mineral density. INTRODUCTION: FGF23 is involved in mineral homeostasis but may also have a role in vascular calcification and bone mineralization. Previous studies related to FGF23 and vascular and bone outcomes have been restricted to dialysis patients. The aim of the present study was to establish whether or not plasma FGF23 is associated with aortic and coronary calcification, arterial stiffness, and bone mineral density in patients with early as well as late stages of CKD. METHODS: In a cohort of 142 patients with CKD stages 2-5D, we made routine biochemistry and intact FGF23 determinations, and assessed aortic and coronary calcification, bone mineral density (BMD), and arterial stiffness by multislice spiral computed tomography and automated pulse wave velocity (PWV). RESULTS: Plasma intact FGF23 levels were elevated in CKD patients; the elevation preceded that of serum phosphate in early-stage CKD. Patients with elevated FGF23 levels had higher aortic and coronary calcification scores than patients with lower FGF23 levels. Multivariate linear regression analysis indicated that only age (p < 0.001) and FGF23 (p = 0.008) were independently associated with aortic calcification score. Plasma FGF23 was neither associated with PWV nor with BMD. CONCLUSION: Our data suggest that plasma FGF23 is an independent biomarker of vascular calcification in patients with various CKD stages including early stages. The association between vascular calcification and FGF23 levels appears to be independent of BMD. It remains to be seen whether this association is independent of bone turnover and bone mass.

High contrast x-ray speckle from atomic-scale order in liquids and glasses.

The availability of ultrafast pulses of coherent hard x rays from the Linac Coherent Light Source opens new opportunities for studies of atomic-scale dynamics in amorphous materials. Here, we show that single ultrafast coherent x-ray pulses can be used to observe the speckle contrast in the high-angle diffraction from liquid Ga and glassy Ni(2)Pd(2)P and B(2)O(3). We determine the thresholds above which the x-ray pulses disturb the atomic arrangements. Furthermore, high contrast speckle is observed in scattering patterns from the glasses integrated over many pulses, demonstrating that the source and optics are sufficiently stable for x-ray photon correlation spectroscopy studies of dynamics over a wide range of time scales.