The fluctuation-dissipation measurement instrument at the Linac Coherent Light Source.

The development of new modes at x-ray free electron lasers has inspired novel methods for studying fluctuations at different energies and timescales. For closely spaced x-ray pulses that can be varied on ultrafast time scales, we have constructed a pair of advanced instruments to conduct studies targeting quantum materials. We first describe a prototype instrument built to test the proof-of-principle of resonant magnetic scattering using ultrafast pulse pairs. This is followed by a description of a new endstation, the so-called fluctuation-dissipation measurement instrument, which was used to carry out studies with a fast area detector. In addition, we describe various types of diagnostics for single-shot contrast measurements, which can be used to normalize data on a pulse-by-pulse basis and calibrate pulse amplitude ratios, both of which are important for the study of fluctuations in materials. Furthermore, we present some new results using the instrument that demonstrates access to higher momentum resolution.

Scaling of domain cascades in stripe and skyrmion phases.

The origin of deterministic macroscopic properties often lies in microscopic stochastic motion. Magnetic fluctuations that manifest as domain avalanches and chaotic magnetization jumps exemplify such stochastic motion and have been studied in great detail. Here we report Fourier space studies of avalanches in a system exhibiting competing magnetic stripe and skyrmion phase using a soft X-ray speckle metrology technique. We demonstrate the existence of phase boundaries and underlying critical points in the stripe and skyrmion phases. We found that distinct scaling and universality classes are associated with these domain topologies. The magnitude and frequency of abrupt magnetic domain jumps observed in the stripe phase are dramatically reduced in the skyrmion phase. Our results provide an incisive way to probe and understand phase stability in systems exhibiting complex spin topologies.

Publisher Correction: Scaling of domain cascades in stripe and skyrmion phases.

The original version of this Article contained an error in Fig. 4d, in which the label of the region to the left of the white dashed lines incorrectly read 'Order stripes'. The correct version states 'Disorder stripes'. This has been corrected in both the PDF and HTML versions of the Article.

Nanosecond X-Ray Photon Correlation Spectroscopy on Magnetic Skyrmions.

We report an x-ray photon correlation spectroscopy method that exploits the recent development of the two-pulse mode at the Linac Coherent Light Source. By using coherent resonant x-ray magnetic scattering, we studied spontaneous fluctuations on nanosecond time scales in thin films of multilayered Fe/Gd that exhibit ordered stripe and Skyrmion lattice phases. The correlation time of the fluctuations was found to differ between the Skyrmion phase and near the stripe-Skyrmion boundary. This technique will enable a significant new area of research on the study of equilibrium fluctuations in condensed matter.

Coupled Skyrmion sublattices in Cu(2)OSeO(3).

We report the observation of a Skyrmion lattice in the chiral multiferroic insulator Cu2OSeO3 using Cu L3-edge resonant soft x-ray diffraction. We observe the unexpected existence of two distinct Skyrmion sublattices that arise from inequivalent Cu sites with chemically identical coordination numbers but different magnetically active orbitals. The Skyrmion sublattices are rotated with respect to each other, implying a long wavelength modulation of the lattice. The modulation vector is controlled with an applied magnetic field, associating this moirélike phase with a continuous phase transition. Our findings will open up a new class of science involving manipulation of quantum topological states.

Mapping spatial and field dependence of magnetic domain memory by soft X-ray speckle metrology.

The occurrence of magnetic domain memory has been observed in ferromagnets, either induced by structural defects or by exchange couplings. Being able to quantify the amount of memory as a function of length scale, field and temperature is both of fundamental and technological importance. A technique has been refined to statistically quantify the magnetic domain memory in ferromagnetic thin films by using coherent soft-X-ray scattering metrology. This technique, based on cross-correlating magnetic speckle patterns, provides a unique way to map out the behavior of domain memory. Here, the details of our correlation method and the necessary treatment of the X-ray scattering images to extract spatial and field dependences in the memory information are reviewed. The resulting correlation maps, measured on [Co/Pd]IrMn multilayers, show how magnetic domain memory evolves at various spatial scales, as a function of the field magnitude throughout magnetization cycles, but also as a function of field cycling and of temperature. This technique can easily be applied to a wide variety of systems presenting memory effects, in soft and hard matter, and also to dynamical studies.

Records on floral biology and visitors of Jacquemontia montana (Moric.) Meisn. (Convolvulaceae) in Mucugê, Bahia.

We present the first records on pollination biology of Jacquemontia montana (Moric.) Meisn. (Convolvulaceae), a widespread climber in the Chapada Diamantina. Our objectives were to (1) characterise flower morphology and biology of J. montana; (2) sample flower visitors and (3) make inferences about potential pollinators, based on foraging behaviour. Observations and sampling were performed on two patches from 8:00 AM to 3:30 PM, May 15th to 16th, 2007. The corolla is bowl shaped, pentamerous, gamopetalous, actinomorphic, and yellow, with a mean diameter of 22.43 +/- 1.81 mm, the depth being variable during flower phases. Stigma receptivity lasted from 8:00 AM-3:30 PM and pollen viability from 9:00 AM-3:30 PM Pollen. showed great decline in number but not in viability during anthesis. Nectarivorous (Coleoptera, Diptera, Hymenoptera) and herbivorous (Orthoptera) insects were found on the flowers. Both male and female bees (Dialictus spp., Robertson 1902) were the most frequent flower visitor. The bees' behaviour, and time spent on flowers, varied according to the resource gathered (i.e., pollen or nectar). The Dialictus species are likely to be the main pollinator of J. montana, considering the frequency, contact with reproductive parts, and carrying only J. montana pollen spread over the ventral part of the thorax, abdomen and legs. Although not quantified, nectar may still be available in the afternoon, considering the behaviour of bees on flowers during this time. Pollen:ovule ration that was1.200:4, suggests facultative xenogamy.

Records on floral biology and visitors of Jacquemontia montana (Moric.) Meisn. (Convolvulaceae) in Mucugê, Bahia / Registros sobre a biologia floral e visitantes de Jacquemontia montana (Moric.) Meisn. (Convolvulaceae) em Mucugê, Bahia

We present the first records on pollination biology of Jacquemontia montana (Moric.) Meisn. (Convolvulaceae), a widespread climber in the Chapada Diamantina. Our objectives were to (1) characterise flower morphology and biology of J. montana; (2) sample flower visitors and (3) make inferences about potential pollinators, based on foraging behaviour. Observations and sampling were performed on two patches from 8:00 AM to 3:30 PM, May 15th to 16th, 2007. The corolla is bowl shaped, pentamerous, gamopetalous, actinomorphic, and yellow, with a mean diameter of 22.43 ± 1.81 mm, the depth being variable during flower phases. Stigma receptivity lasted from 8:00 AM-3:30 PM and pollen viability from 9:00 AM-3:30 PM Pollen. showed great decline in number but not in viability during anthesis. Nectarivorous (Coleoptera, Diptera, Hymenoptera) and herbivorous (Orthoptera) insects were found on the flowers. Both male and female bees (Dialictus spp., Robertson 1902) were the most frequent flower visitor. The bees' behaviour, and time spent on flowers, varied according to the resource gathered (i.e., pollen or nectar). The Dialictus species are likely to be the main pollinator of J. montana, considering the frequency, contact with reproductive parts, and carrying only J. montana pollen spread over the ventral part of the thorax, abdomen and legs. Although not quantified, nectar may still be available in the afternoon, considering the behaviour of bees on flowers during this time. Pollen:ovule ration that was1.200:4, suggests facultative xenogamy.

Apresentamos os primeiros registros sobre a biologia da polinização de Jacquemontia montana (Moric.) Meisn. (Convolvulaceae), uma trepadeira com ampla distribuição na Chapada Diamantina, Bahia. Os objetivos deste estudo foram: (1) caracterizar a morfologia e biologia floral; (2) amostrar os visitantes; e (3) inferir os possíveis polinizadores, baseando-se no comportamento de forrageio. Observações e amostragens foram conduzidas em duas manchas das 8:00 às 15:30 horas, nos dias 15 e 16 de maio de 2007. A corola é amarela, tem forma de disco, pentâmera, gamopétala, actinomorfa. A corola exposta tem largura média de 22,43 ± 1,81 mm. A receptividade estigmática ocorre das 8:00 às 15:30 horas e a viabilidade polínica das 9:00 às 15:30 horas, se sobrepondo fortemente. O pólen, porém, apresentou forte declínio em número, devido à retirada pelos visitantes, mas não em viabilidade durante a antese. Insetos nectarívoros (Coleoptera, Diptera, Hymenoptera) e herbívoros (Orthoptera) visitaram as flores. Hymenoptera incluiu representantes das famílias Formicidae (formigas) e Halictidae (Dialictus spp.). Machos e fêmeas de Dialictus spp. foram os visitantes mais frequentes. O comportamento e duração das visitas dessas abelhas variaram conforme o recurso coletado (i.e., pólen ou néctar). As espécies de Dialictus foram os polinizadores potenciais de J. montana, considerando sua frequência, contato com órgãos reprodutivos, e pelo fato de carregar apenas pólen de J. montana na superfície ventral do tórax, abdome e pernas. Embora não tenha sido quantificado, o néctar deve estar disponível até o final da tarde, considerando o comportamento das abelhas nas flores nesse período. A relação pólen:óvulo, no valor de 1.200:4, sugere a ocorrência de xenogamia facultativa.

Controlling the magnetic ground state in Cr1-x Vx films.

We demonstrate the ability to control the magnetic phase diagram of Cr1-x Vx(110) thin films grown on a W(110) substrate. Using angle-resolved photoemission, we have mapped paramagnetic and commensurate and incommensurate antiferromagnetic phases as a function of temperature, film thickness, and composition. We show that surface-localized electron states play a key role in the observed phase behaviors and suggest from this that it might be possible to control the magnetic phase by applying an external electric field.

Disorder-induced microscopic magnetic memory.

Using coherent x-ray speckle metrology, we have measured the influence of disorder on major loop return point memory (RPM) and complementary point memory (CPM) for a series of perpendicular anisotropy Co/Pt multilayer films. In the low disorder limit, the domain structures show no memory with field cycling--no RPM and no CPM. With increasing disorder, we observe the onset and the saturation of both the RPM and the CPM. These results provide the first direct ensemble-sensitive experimental study of the effects of varying disorder on microscopic magnetic memory and are compared against the predictions of existing theories.

Mechanism of gap opening in a triple-band Peierls system: in atomic wires on Si.

One dimensional (1D) metals are unstable at low temperature undergoing a metal-insulator transition coupled with a periodic lattice distortion, a Peierls transition. Angle-resolved photoemission study for the 1D metallic chains of In on Si(111), featuring a metal-insulator transition and triple metallic bands, clarifies in detail how the multiple band gaps are formed at low temperature. In addition to the gap opening for a half-filled ideal 1D band with a proper Fermi surface nesting, two other quasi-1D metallic bands are found to merge into a single band, opening a unique but k-dependent energy gap through an interband charge transfer. This result introduces a novel gap-opening mechanism for a multiband Peierls system where the interband interaction is important.

Indium square root 7 x square root 3 on Si(111): a nearly free electron metal in two dimensions.

We present measurements of the Fermi surface and underlying band structure of a single layer of indium on Si(111) with square root 7 x square root 3 periodicity. Electrons from both indium valence electrons and silicon dangling bonds contribute to a nearly free, two-dimensional metal on a pseudo-4-fold lattice, which is almost completely decoupled at the Fermi level from the underlying hexagonal silicon lattice. The mean free path inferred from our data is quite long, suggesting the system might be a suitable model for studying the ground state of two-dimensional metals.

Unusual spectral behavior of charge-density waves with imperfect nesting in a quasi-one-dimensional metal.

Low-temperature electronic properties of the charge-density-wave system NbSe3 are reported from angle-resolved photoemission at 15 K. The effect of two instabilities q(1) and q(2) on the k-resolved spectral function is observed for the first time. With a pseudogap background, the gap spectra exhibit maxima at Delta*(1) approximately 110 meV and Delta*(2) approximately 45 meV. Imperfectly nested sections of the Fermi surface lack a Fermi-Dirac edge, and show the signature of a dispersion that is modified by self-energy effects. The energy scale is of the order of the effective gap 2 Delta*(2). The effect disappears above T2, suggesting a correlation with the charge-density-wave state.

Spin-resolved photoemission of surface states of W(110)-(1 x 1)H.

The surface electronic states of W(110)-(1 x 1)H have been measured using spin- and angle-resolved photoemission. We directly demonstrate that the surface bands are both split and spin-polarized by the spin-orbit interaction in association with the loss of inversion symmetry near a surface. We observe 100% spin polarization of the surface states, with the spins aligned in the plane of the surface and oriented in a circular fashion relative to the Smacr; symmetry point. In contrast, no measurable polarization of nearby bulk states is observed.

Differential photoelectron holography: a new approach for three-dimensional atomic imaging.

We propose differential holography as a method to overcome the long-standing forward-scattering problem in photoelectron holography and related techniques for the three-dimensional imaging of atoms. Atomic images reconstructed from experimental and theoretical Cu 3p holograms from Cu(001) demonstrate that this method suppresses strong forward-scattering effects so as to yield more accurate three-dimensional images of side- and backscattering atoms.

High-temperature symmetry breaking in the electronic band structure of the quasi-one-dimensional solid NbSe3.

The electronic band structure of the Peierls compound NbSe3 has been explored for its symmetries with microspot synchrotron photoemission. The Fermi level crossings and deviations from one-dimensional behavior are identified. Density-functional calculations of the Fermi surfaces confirm the nesting conditions relevant for the two phase transitions. The instability along the chains with superstructure periodicity q = 0.44 A(-1) induces a backfolding of the electronic bands, and the Fermi level crossings appear suppressed. This broken symmetry is observed in the fluctuation regime at more than twice the critical temperature, where the correlation length is strongly reduced.

Effects of age and coion (K+ and Na+) on the toxicity of thiocyanate to rainbow trout (Oncorhynchus mykiss) during pulse or continuous exposure.

Thiocyanate (SCN-) is released to the aquatic environment as a result of the treatment of cyanide-bearing wastes from precious-metal mining activity. During continuous exposure alevin rainbow trout (1- and 10-day-old) were approximately 90% more tolerant of SCN- than juveniles (2-month-old). Pulse exposure of alevins for periods > or = 48 hr were required before postexposure stress reduced tolerance (by approximately 30%) in the 24-hr period following exposure. In contrast, stressing of juveniles after exposures of > or= 9 hr consistently reduced tolerance by approximately 60%. While coion (K+ or Na+ for SCN- derived from either KSCN or NaSCN) had no influence on SCN- toxicity for alevins, juveniles exhibited reduced tolerance in the presence on Na+. Although sudden death syndrome was apparent in juveniles, none occurred with alevins. Overall, juveniles were less tolerant of SCN- than alevins, possibly because of the enhanced efficiency of SCN- uptake by gill respiration versus the predominantly vitelline membrane respiration of alevins.

Time-resolved electron energy loss spectroscopy.

Two recent instrumental improvements in high-resolution electron energy loss spectroscopy make possible the recording of complete surface vibrational spectra on the millisecond time scale. This is the first spectroscopic probe capable of directly measuring fundamental surface rate processes in real time with a resolution less than or equal to 1 millisecond. Such measurements are the key to understanding surface kinetics at the molecular level. This article summarizes experiments on the adsorption and decomposition of formic acid on Cu(100) to investigate the temperature and coverage dependence of the formate intermediate. Other results are cited that provide a detailed description of the decomposition of methanol on Ni(110). Also reported are direct measurements of the residence time of carbon monoxide on Cu(100) and the associated desorption kinetics.

Normal emission photoelectron diffraction studies at Stanford Synchrotron Radiation Laboratory.

A series of experiments designed to characterize the surface structural sensitivity of photoelectron diffraction (PhD) is described. The technique's relation to low energy electron diffraction and to surface extended x-ray absorption fine structure (SEXAFS) is explored, and useful comparisons with the latter are pointed out. The application of normal emission photoelectron diffraction to disordered overlayers is shown to be reasonably straightforward. Data on both 2-D and 3-D (multiple-site) disordered overlayers are presented. The localized atom-specific nature of PhD is shown to lend the technique real potential in the study of molecular adsorbate systems.