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Some X-ray free-electron laser facilities are pushing towards sub-10 fs pulses, making it desirable to reduce errors in X-ray/optical delay measurements to the 1 fs level. Researchers have now demonstrated X-ray measurements with a temporal resolution shorter than 1 fs, opening up new possibilities for time-resolved X-ray experiments. Today's brightest coherent X-ray sources, X-ray free-electron lasers, produce ultrafast X-ray pulses for which full-width at half-maximum durations as short as 3 fs have been measured 1 . There has been a marked increase in the popularity of such short pulses now that optical timing techniques have begun to report an X-ray/optical delay below ∼10 fs r.m.s. errors. As a result, sub-10 fs optical pulses have been implemented at the Linac Coherent Light Source (LCLS) X-ray beamlines, thus warranting a push to reduce the error in X-ray/optical delay measurements to the 1 fs level. Here, we report a unique two-dimensional spectrogram measurement of the relative X-ray/optical delay. This easily scalable relative delay measurement already surpasses previous techniques by an order of magnitude with its sub-1 fs temporal resolution and opens up the prospect of time-resolved X-ray measurements to the attosecond community.

Sponges are probably the earliest branching animals and their fossil record dates back to the Precambrian. Identifying their skeletal structure and composition is thus a crucial step in improving our understanding of the early evolution of metazoans. Here, we present the discovery of 505–million-year-old chitin, found in exceptionally well preserved Vauxia gracilenta sponges from the Middle Cambrian Burgess Shale. Our new findings indicate that, given the right fossilization conditions, chitin is stable for much longer than previously suspected. The preservation of chitin in these fossils opens new avenues for research into other ancient fossil groups.

Many-body interactions in crystalline solids can be conveniently described in terms of quasiparticles with strongly renormalized masses as compared with those of non-interacting particles. Examples of extreme mass renormalization are on the one hand graphene, where the charge carriers obey the linear dispersion relation of massless Dirac fermions, and on the other hand heavy-fermion materials where the effective electron mass approaches the mass of a proton. Here we show that both extremes, Dirac fermions, like they are found in graphene and extremely heavy quasiparticles characteristic for Kondo materials, may not only coexist in a solid but can also undergo strong mutual interactions. Using the example of EuRh 2 Si 2 , we explicitly demonstrate that these interactions can take place at the surface and in the bulk. The presence of the linear dispersion is imposed solely by the crystal symmetry, whereas the existence of heavy quasiparticles is caused by the localized nature of the 4 f states. The interactions of quasiparticles can be described by renormalizing their masses, such that some materials have a vanishingly small effective mass, whereas others have a very high effective mass. The observation by Vyalikh and colleagues of both extremes occurring on the surface and interior of the same material offers a new view of many-body interactions.

The European X-ray Free-Electron Laser (EuXFEL) Facility is the leading international scientific center for studying the structure and properties of materials using coherent X-rays with high temporal and spatial resolution. The results of the collaboration of the EuXFEL experts and the researchers of the ITMO University in 2015–2022 are briefly described. The unique possibilities of the EuXFEL are demonstrated by an example of studying the ultrafast magnetic dynamics by the researchers of the ITMO University in 2019.

The structure of native Champsocephalus gunnari icefish otoliths, scales, teeth, bones and pristine hydroxyapatite (HA) were examined using Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. NEXAFS Cls-absorption spectra of the selected icefish hard tissues indicate that otoliths contain anion [CO3]2-. NEXAFS P2p-spectra clearly indicate the absence of phosphorus atoms only within otoliths and scales samples. However, the icefish teeth and bones P2p-spectra demonstrate identical spectral feature typical for the HA. NEXAFS Ca2p-spectra of the icefish hard tissues studied also shows features, which are in good correspondence with HA spectra. Interestingly, there is a red shift ≈ 0.1 eV of the 2p1/2,3/2 → 3d transition energies in NEXAFS Ca2p-spectra of teethes and bones of the C. gunnari in comparison to HA.

The electronic structure of shandite Co3Sn2S2 was determined by photoelectron spectroscopy and compared with ab initio band structure calculations. Presented results give evidence that this compound has half-metallic ferromagnetic properties.

A composite material based on MWCNT covered by pyrolytic Cr has been prepared by MOCVD growth technique using bis(arene)chromium compounds as the pyrolytic Cr source. Their structures and morphologies were preliminary studied by X-ray diffraction and scanning and scanning electron microscopy. The atomic and chemical composition of the interface, MWCNT surface and Cr-coating of the composite were studied by total electron yield mode in the range NEXAFS C1s - and Cr2p - absorption edge with use of synchrotron radiation of RGBL at BESSY-II. The study has shown that top layers of the MWCNT in composite have no essential destruction, the coating of the MWCNT surfaces is continuous and consists of Cr2O3. The chromium oxide adhesion is provided by chemical binding between the carbon atoms of the MWCNT top layer and the oxygen atoms of the coating.

High resolution angle-resolved photoemission of quasi-2D KMo6O17 purple bronze has been performed in the range from room temperature to 130 K, slightly above the charge density wave (CDW) transition (Tc 110 K), and down to 35 K (well below Tc). In this paper we report a detailed study of how electronic band structure is affected by this transition driven by the hidden nesting scenario. The expected spectroscopic fingerprints of the CDW phase transition have been found and discussed according to the hidden one dimension and the development of a quasi-commensurate CDW. The excellent agreement between theory and our experimental results makes of potassium purple bronze a reference system for studying this type of instabilities.

Here we present applications of the periodic Anderson model (PAM) to consideration of wave vector (k)- and spin-dependent hybridization effects in Ce metal. It was shown that k-dependent splitting of the 4f ionization peak of Ce/W(1 10) are correctly described in the framework of the PAM (Coulomb repulsion between two f electrons localized on the same lattice site Uff→ ). Our results show that the wave vector is conserved upon hybridization. In case of the magnetically ordered Ce monolayer, spin- and angle-resolved resonant photoemission spectra reveal spin-dependent changes of the Fermi-level peak intensities (which reflect the hybridization strength). That indicate a spin-dependence of 4f hybridization and, thus, of 4f occupancy and local moment. The phenomenon was also described in the framework of PAM by 4f electron hopping into the exchange split Fe 3d derived bands that form a spin-gap at the Fermi energy around the T point of the surface Brillouin zone.

In the present contribution we report on the results of the angle-resolved photoemission (PE) studies of thin layers of Yb (1–3 ML-thick) on W(110) surface. The clear splitting of the Yb 4f7/2 state was observed in the PE spectra measured around point for 1 ML-thick Yb film. The measured PE spectra were analyzed by means of the simplified periodic Anderson model.