The concepts and technical realisation of the high-resolution soft X-ray beamline ADRESS operating in the energy range from 300 to 1600 eV and intended for resonant inelastic X-ray scattering (RIXS) and angle-resolved photoelectron spectroscopy (ARPES) are described. The photon source is an undulator of novel fixed-gap design where longitudinal movement of permanent magnetic arrays controls not only the light polarization (including circular and 0-180 rotatable linear polarizations) but also the energy without changing the gap. The beamline optics is based on the well established scheme of planegrating monochromator operating in collimated light. The ultimate resolving power E/ÁE is above 33000 at 1 keV photon energy. The choice of blazed versus lamellar gratings and optimization of their profile parameters is described. Owing to glancing angles on the mirrors as well as optimized groove densities and profiles of the gratings, the beamline is capable of delivering high photon flux up to 1 Â 10 13 photons s À1 (0.01% BW) À1 at 1 keV. Ellipsoidal refocusing optics used for the RIXS endstation demagnifies the vertical spot size down to 4 mm, which allows slitless operation and thus maximal transmission of the highresolution RIXS spectrometer delivering E/ÁE > 11000 at 1 keV photon energy. Apart from the beamline optics, an overview of the control system is given, the diagnostics and software tools are described, and strategies used for the optical alignment are discussed. An introduction to the concepts and instrumental realisation of the ARPES and RIXS endstations is given.

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Soft-X-ray angle-resolved photoelectron spectroscopy (ARPES) with photon energies around 1 keV combines the momentum space resolution with increasing probing depth. The concepts and technical realisation of the new soft-X-ray ARPES endstation at the ADRESS beamline of SLS are described. The experimental geometry of the endstation is characterized by grazing X-ray incidence on the sample to increase the photoyield and vertical orientation of the measurement plane. The vacuum chambers adopt a radial layout allowing most efficient sample transfer. High accuracy of the angular resolution is ensured by alignment strategies focused on precise matching of the X-ray beam and optical axis of the analyzer. The high photon flux of up to 10(13) photons s(-1) (0.01% bandwidth)(-1) delivered by the beamline combined with the optimized experimental geometry break through the dramatic loss of the valence band photoexcitation cross section at soft-X-ray energies. ARPES images with energy resolution up to a few tens of meV are typically acquired on the time scale of minutes. A few application examples illustrate the power of our advanced soft-X-ray ARPES instrumentation to explore the electronic structure of bulk crystals with resolution in three-dimensional momentum, access buried heterostructures and study elemental composition of the valence states using resonant excitation.

We investigate magnetic excitations in the spin-ladder compound Sr 14 Cu 24 O 41 using high-resolution Cu L 3 edge resonant inelastic x-ray scattering (RIXS). Our findings demonstrate that RIXS couples to two-triplon collective excitations. In contrast to inelastic neutron scattering, the RIXS cross section changes only moderately over the entire Brillouin zone, revealing high sensitivity also at small momentum transfers, allowing determination of the two-triplon energy gap as 100 AE 30 meV. Our results are backed by calculations within an effective Hubbard model for a finite-size cluster, and confirm that optical selection rules are obeyed for excitations from this spherically symmetric quantum spin-liquid ground state. DOI: 10.1103/PhysRevLett.103.047401 PACS numbers: 78.70.En, 71.10.Pm, 75.25.+z, 75.30.Ds Collective excitations in strongly correlated electron materials remain a pivotal challenge in contemporary solid state physics. It is widely debated whether magnetic excitations provide the pairing interaction in the hightemperature and unconventional superconductors [1,2]. From that perspective quantum spin systems attract considerable interest. While most such materials, e.g., the cuprate superconductors, exhibit enormous complexity, the two-leg spin ladder is easier to tract theoretically [3][4][5][6]. It consists of two parallel chains (legs) with a transverse (rung) exchange coupling. This system features a singlet ground state and dispersive triplet excitations (triplons), that both have quantum mechanical origin without any classical counterpart. To date, mainly two techniques have been established as momentum-and energy-resolved probes of the dispersion of collective excitations: angleresolved photoelectron spectroscopy and inelastic neutron scattering (INS) for charge and spin degrees of freedom, respectively [7,8]. Because of the latest instrumental improvements [9,10], the energy scale of magnetic exchange is becoming readily accessible for resonant inelastic x-ray scattering (RIXS) [11][12][13][14], which is promising to give information on both, spin and charge degrees of freedom, and in addition is an element-specific technique. Furthermore, RIXS requires only small sample volumes (<0:1 mm 3 ). Recent RIXS studies were performed on long-range ordered magnets with spin-wave excitations [15][16][17].In this Letter, we report a study of the two-leg quantum spin ladder Sr 14 Cu 24 O 41 [18,19] by means of momentumresolved high-resolution RIXS at the Cu L 3 edge. Given that Cu L 3 scattering experiments have been already shown to contain valuable information about the charge degrees of freedom [20], an outstanding question we would like to address here is: how can RIXS provide information on magnetic excitations from a quantum ground state. In the ladder system of Sr 14 Cu 24 O 41 no symmetry breaking occurs-neither in spin-nor in real-space-in contrast to, e.g., a magnetically ordered state, where both symmetries are broken and the direction of the ordered moments dictates the quantization axi...

We present high resolution (DeltaE=120 meV) resonant inelastic x-ray scattering data measured at the Ni L3 edge (2p_{3/2}-->3d) on the paradigmatic antiferromagnetic oxide NiO. Spectra reveal clear signatures of magnetic excitations at approximately 95 and approximately 190 meV whose energy seems independent from transferred momentum. These spectral features are well reproduced by a single Ni2+ ion model in an effective exchange field. Within this local model the two magnetic excitations are characterized by a variation of the atomic magnetic moment along the local ordering direction (DeltaS_{alpha}) of one and two units. The DeltaS_{alpha}=2 case has different nature from bimagnons observed in optical Raman spectra, for which DeltaS_{alpha}=0.

We studied the neutral electronic excitations of NiO localized at the Ni sites by measuring the resonant inelastic x-ray scattering (RIXS) spectra at the Ni M2,3 edges. The good energy resolution allows an unambiguous identification of several spectral features due to excitations. The dependence of the RIXS spectra on the excitation energy gives evidence of local spin flip and yields a value of 125 +/- 15 meV for the antiferromagnetic exchange interaction. Accurate crystal field parameters are also obtained.

Crystal Growth & DesignCOMMUNICATION together with the beamline automation at X06DA, this is a clear step toward a much more streamlined and successful work-flow in macromolecular crystallography, eliminating significant bottlenecks in the process.' ASSOCIATED CONTENT b S Supporting Information. Movie showing the workflow and isXds at the SLS crystallization platform at beamline X06DA. This material is available free of charge via the Internet at http:// pubs.acs.org.

For many scientific questions gaining three-dimensional insight into a specimen can provide valuable information. We here present an instrument called "tOMography Nano crYo (OMNY)," dedicated to high resolution 3D scanning x-ray microscopy at cryogenic conditions via hard X-ray ptychography. Ptychography is a lens-less imaging method requiring accurate sample positioning. In OMNY, this in achieved via dedicated laser interferometry and closed-loop position control reaching sub-10 nm positioning accuracy. Cryogenic sample conditions are maintained via conductive cooling. 90 K can be reached when using liquid nitrogen as coolant, and 10 K is possible with liquid helium. A cryogenic sample-change mechanism permits measurements of cryogenically fixed specimens. We compare images obtained with OMNY with older measurements performed using a nitrogen gas cryo-jet of stained, epoxy-embedded retina tissue and of frozen-hydrated Chlamydomonas cells.