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In the novel stoichiometric iron-based material RbEuFe4As4 superconductivity coexists with a peculiar long-range magnetic order of Eu 4f states; their coexistance is puzzling and represents a challenge for both experiment and theory. Using angle-resolved photoemission spectroscopy, resonant photoemission spectroscopy, Andreev reflection spectroscopy and scanning tunneling spectroscopy we have addressed this puzzle and unambigously shown that Fe- and Eu-derived states are largely decoupled and that superconducting and a long range magnetic orders exist almost independently from each other.

In pnictide RbEuFe4As4, superconductivity sets in at 36 K and coexists, below 15-19 K, with the long-range magnetic ordering of Eu 4f spins. Here we report scanning tunneling experiments performed on cold-cleaved single crystals of the compound. The data revealed the coexistence of large Rb-Terminated and small Eu-Terminated terraces, both manifesting 1 × 2 and 2×2 reconstructions. On 2×2 surfaces, a hidden electronic order with a period â 5 nm was discovered. A superconducting gap of â 7 meV was seen to be strongly filled with quasiparticle states. The tunneling spectra compared with density functional theory calculations confirmed that flat electronic bands due to Eu 4f orbitals are situated â 1.8 eV below the Fermi level and thus do not contribute directly to Cooper pair formation.

Typically, topological superconductivity is reachable via proximity effect by a direct deposition of superconductor (S) on top of a topological insulator (TI) surface. Here we observed and analyzed the double critical current in the Josephson junctions based on the topological insulator in the fabricated planar Superconducting Quantum Interference Device. By measuring critical currents as a function of temperature and magnetic field, we show that the second critical current stems from the intrinsic superconductivity of the S/TI interface, which is supported by the modified Resistively Shunted Junction model and Transmission Electron Microscopy studies. This complex structure of the interface should be taken into account when technological process involves Ar-plasma cleaning.

The development of materials that are non-magnetic in the bulk but exhibit two-dimensional (2D) magnetism at the surface is at the core of spintronics applications. Here, we present the valence-fluctuating material EuIrSi, where in contrast to its non-magnetic bulk, the Si-terminated surface reveals controllable 2D ferromagnetism. Close to the surface the Eu ions prefer a magnetic divalent configuration and their large 4f moments order below 48 K. The emerging exchange interaction modifies the spin polarization of the 2D surface electrons originally induced by the strong Rashba effect. The temperature-dependent mixed valence of the bulk allows to tune the energy and momentum size of the projected band gaps to which the 2D electrons are confined. This gives an additional degree of freedom to handle spin-polarized electrons at the surface. Our findings disclose valence-fluctuating rare-earth based materials as a very promising basis for the development of systems with controllable 2D magnetic properties which is of interest both for fundamental science and applications., This work was supported by the German Research Foundation (DFG) through Grants No. KR3831/5-1, No. LA655/20-1 and Fermi-NEst. Support was provided by the Spanish Ministry of Science, Innovation and Universities (Project No. FIS2016-76617-P and No. FIS2016-75862-P). We acknowledge financial support from the Spanish Ministry of Economy (MAT-2017-88374-P). The authors also acknowledge support by Saint Petersburg State University (Grant No. 15.61.202.2015) and Tomsk State University Academic D. I. Mendeleev Fund Program (Research Grant No. 8.1.01.2018). We acknowledge Diamond Light Source for access to beamline I05 (proposals no. SI18844-1 and SI17761-1) that contributed to the results presented here.

It was shown, that the treatment of graphite oxide (GO) at a temperature of 1000 °C and a static pressure of 500 bar recovers the graphene layers. Addition of triphenylphosphine to GO helps in removal of oxygen during the treatment and allows introducing ca. 0.7 at% of phosphorus in the product. Most phosphorus atoms are bonded with oxygen as the 31P nuclear magnetic resonance spectrum showed. An analysis of the X-ray photoelectron P 2p spectrum additionally found the components corresponding to C P and P P bonding. Assembling of phosphorus atoms into nanometer clusters was confirmed by transmission electron microscopy. Raman spectroscopy and electrical conductivity measurements revealed the n-type doping of graphitic material through the incorporation of phosphorus.

One of the approaches to tackle the problem of limited electrolyte electrochemical stability, which controls the development of novel electrochemical storage devices, is the use of solid electrolytes. Here, we focus on one of the most promising among oxide-based glass-ceramic materials, Li1+xAlxGe2−xP3O12, to investigate the physical and chemical mechanisms that govern the enhancement of Li-conductivity upon variation of its composition and glass crystallization conditions during a two-step heat treatment. Using X-ray and neutron diffraction, small-angle neutron scattering and Raman spectroscopy we found that the addition of 6–18 mol% yttria makes the polyphosphate chains in glass more thermally stable. This leads to sudden and uniform glass crystallization over the whole volume. This peculiar glass structure governs the further crystallization behavior and ensures the optimal organization of intergrain boundaries. The highest Li-conductivity is achieved for a sample with 12 mol% yttria annealed for 2 hours at 750 °C. In addition, nuclear magnetic resonance together with bond valence sum analysis provides further insight into atomistic mechanisms of ionic conductivity in NASICON-based lithium-conductive ceramics.

In the novel stoichiometric iron-based material ${\mathrm{RbEuFe}}_{4}{\mathrm{As}}_{4}$, superconductivity coexists with a peculiar long-range magnetic order of Eu 4f states. Using angle-resolved photoemission spectroscopy, we reveal a complex three-dimensional electronic structure and compare it with density functional theory calculations. Multiple superconducting gaps were measured on various sheets of the Fermi surface. High-resolution resonant photoemission spectroscopy reveals magnetic order of the Eu 4f states deep into the superconducting phase. Both the absolute values and the anisotropy of the superconducting gaps are remarkably similar to the sibling compound without Eu, indicating that Eu magnetism does not affect the pairing of electrons. A complete decoupling between Fe- and Eu-derived states was established from their evolution with temperature, thus unambiguously demonstrating that superconducting and a long-range magnetic orders exist independently from each other. The established electronic structure of ${\mathrm{RbEuFe}}_{4}{\mathrm{As}}_{4}$ opens opportunities for the future studies of the highly unorthodox electron pairing and phase competition in this family of iron-based superconductors with doping.

In a Kondo lattice, the Luttinger theorem requires the $f$ electron degree of freedom to enter the Fermi volume in the strong-coupling regime, while the $f$ electron remains nearly localized. A common hypothesis assumes that the Fermi volume shrinks with increasing temperature when the $f$ electron decouples from the Fermi surface with the breakdown of the Kondo lattice effect. However, experimental evidence for this phenomen is still very scarce. Here, the authors demonstrate the reconstruction of the Fermi surface between 14 and 300 K from $l\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}e$ to $s\phantom{\rule{0}{0ex}}m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}l$ in the prototypical Kondo lattice YbRh${}_{2}$Si${}_{2}$ by Compton scattering.

We present a combined experimental and theoretical study of the two-dimensional electron states at the iridium-silicide surface of the antiferromagnet GdIr2Si2 above and below the Neel temperature. Using angle-resolved photoemission spectroscopy (ARPES) we find a significant spin-orbit splitting of the surface states in the paramagnetic phase. By means of ab initio density-functional-theory (DFT) calculations we establish that the surface electron states that reside in the projected band gap around the M¯ point exhibit very different spin structures which are governed by the conventional and the cubic Rashba effect. The latter is reflected in a triple spin winding, i.e., the surface electron spin reveals three complete rotations upon moving once around the constant energy contours. Below the Neel temperature, our ARPES measurements show an intricate photoemission intensity picture characteristic of a complex magnetic domain structure. The orientation of the domains, however, can be clarified from a comparative analysis of the ARPES data and their DFT modeling. To characterize a single magnetic domain picture, we resort to the calculations and scrutinize the interplay of the Rashba spin-orbit coupling field with the in-plane exchange field, provided by the ferromagnetically ordered 4f moments of the near-surface Gd layer. (Less)

Discovered in 1962, the divalent ferromagnetic semiconductor EuS (TC = 16.5 K, Eg = 1.65 eV) has remained constantly relevant to the engineering of novel magnetically active interfaces, heterostructures, and multilayer sequences and to combination with topological materials. Because detailed information on the electronic structure of EuS and, in particular, its evolution across TC is not well-represented in the literature but is essential for the development of new functional systems, the present work aims at filling this gap. Our angle-resolved photoemission measurements complemented with first-principles calculations demonstrate how the electronic structure of EuS evolves across a paramagnetic–ferromagnetic transition. Our results emphasize the importance of the strong Eu 4f–S 3p mixing for exchange-magnetic splittings of the sulfur-derived bands as well as coupling between f and d orbitals of neighboring Eu atoms to derive the value of TC accurately. The 4f–3p mixing facilitates the coupling between 4f and 5d orbitals of neighboring Eu atoms, which mainly governs the exchange interaction in EuS., This work was supported by the German Research Foundation (DFG) through Grant No. KR3831/5-1, No. LA655/20-1, No. SFB1143 (Project No. 247310070), and No. TRR288 (422213477, project A03). We acknowledge support from the Russian Foundation for Basic Research (Grant No. 20-32-70127) and Saint-Petersburg State University (Grant No. ID 73028629). S.V.E. acknowledges support from a government research assignment for ISPMS SB RAS (Project FWRW-2019-0032). We acknowledge MAX-IV Laboratory for time on the Bloch Beamline under Proposal 20190824. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research council under contract 2018-07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas under contract 2019-02496. The research has also been supported by the project CALIPSO plus under Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020.

Ultrafast manipulation of magnetism bears great potential for future information technologies. While demagnetization in ferromagnets is governed by the dissipation of angular momentum(1-3), materials with multiple spin sublattices, for example antiferromagnets, can allow direct angular momentum transfer between opposing spins, promising faster functionality. In lanthanides, 4f magnetic exchange is mediated indirectly through the conduction electrons(4) (the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction), and the effect of such conditions on direct spin transfer processes is largely unexplored. Here, we investigate ultrafast magnetization dynamics in 4f antiferromagnets and systematically vary the 4f occupation, thereby altering the magnitude of the RKKY coupling energy. By combining time-resolved soft X-ray diffraction with ab initio calculations, we find that the rate of direct transfer between opposing moments is directly determined by this coupling. Given the high sensitivity of RKKY to the conduction electrons, our results offer a useful approach for fine tuning the speed of magnetic devices. By exploring ultrafast magnetization in several compounds with similar crystal structures but different 4f magnetic elements, the authors show that the Ruderman-Kittel-Kasuya-Yosida interaction controls the spin dynamics.

We present and discuss the methodology for modeling $4f$ photoemission spectra, $4f$ photoelectron diffraction (PED) patterns, and magnetic dichroism effects for rare-earth-based materials. Using PED and magnetic dichroism in photoemission, we explore the electronic and magnetic properties of the near-surface region of the valence-fluctuating material ${\mathrm{EuIr}}_{2}{\mathrm{Si}}_{2}$. For the Eu-terminated surface, we found that the topmost Eu layer is divalent and exhibits a ferromagnetic order below 10 K. The valency of the next Eu layer, that is the fifth atomic layer, is about 2.8 at low temperature that is close to the valency in the bulk. The properties of the Si-terminated surface are drastically different. The first subsurface Eu layer (fourth atomic layer below the surface) behaves divalently and orders ferromagnetically below 48 K. Experimental data indicate, however, that there is an admixture of trivalent Eu in this layer, resulting in its valency of about 2.1. The next deeper lying Eu layer (eighth atomic layer below the surface) behaves mixed valently, but the estimated valency of 2.4 is notably lower than the value in the bulk. The presented approach and obtained results create a background for further studies of exotic surface properties of $4f$-based materials, and allow us to derive information related to valency and magnetism of individual rare-earth layers in a rather extended area near the surface.

Antiferromagnets may hold potential as spintronic devices due to their robustness to external magnetic fields, if a suitable control method is realised. Here, a transient rotation of the global spin arrangement of GdRh(2)Si(2)is demonstrated via femtosecond optical excitation. A central prospect of antiferromagnetic spintronics is to exploit magnetic properties that are unavailable with ferromagnets. However, this poses the challenge of accessing such properties for readout and control. To this end, light-induced manipulation of the transient ground state, e.g. by changing the magnetic anisotropy potential, opens promising pathways towards ultrafast deterministic control of antiferromagnetism. Here, we use this approach to trigger a coherent rotation of the entire long-range antiferromagnetic spin arrangement about a crystalline axis in GdRh(2)Si(2)and demonstrate deterministic control of this rotation. Our observations can be explained by a laser-induced shift of the direction of the Gd spins' local magnetic anisotropy, and allow for a quantitative description of the transient magnetic anisotropy potential.

Spin-orbit interaction and structure inversion asymmetry in combination with magnetic ordering is a promising route to novel materials with highly mobile spin-polarized carriers at the surface. Spin-resolved measurements of the photoemission current from the Si-terminated surface of the antiferromagnet TbRh2Si2 and their analysis within an ab initio one-step theory unveil an unusual triple winding of the electron spin along the fourfold-symmetric constant energy contours of the surface states. A two-band k⋅p model is presented that yields the triple winding as a cubic Rashba effect. The curious in-plane spin-momentum locking is remarkably robust and remains intact across a paramagnetic-antiferromagnetic transition in spite of spin-orbit interaction on Rh atoms being considerably weaker than the out-of-plane exchange field due to the Tb 4f moments., This work was supported by the German Research Foundation (Grants No. KR-3831/5-1, No. LA655/20-1, GRK1621, Fermi-NESt No. ANR-16-CE92-0018, and SFB1143, project-id 247310070) and the Spanish Ministry of Science, Innovation, and Universities (Grant Nos. FIS2016-76617-P and MAT-2017-88374-P). We also acknowledge funding from the Department of Education of the Basque government (Grant No. IT1164-19), St. Petersburg State University (Project ID 51126254), and the Russian Foundation for Basic Research (Grant No. 20-32-70127). The SR-ARPES experiments at HiSOR were performed with the approval of the Proposal Assessing Committee of the Hiroshima Synchrotron Radiation Center (Proposal No. 18BG023). We also acknowledge the Impuls-und Vernetzungsfonds der Helmholtz Gemeinschaft (Grant No. HRSF-0067)

The emergence of ferromagnetism in Rashba systems, where the evolving exchange interaction enters into competition with spin-orbit coupling, leads to a nontrivial spin-polarized electronic landscape with an intricate momentum-dependent spin structure, which is challenging to unveil. Here, we show a way to disentangle the contributions from the effective spin-orbit and exchange fields and thus to gain knowledge of the spin structure in ferromagnetic Rashba materials, which is required for spintronic applications. Our approach is based exclusively on spin-integrated photoemission measurements combined with a two-band modeling. As an example, we consider the mixed-valent material EuIr2Si2 which, while being nonmagnetic in the bulk, reveals strong ferromagnetism at the iridium-silicide surface where both spin-orbit and exchange magnetic interactions coexist. The combined effect of these interactions causes a complex band dispersion of the surface state which can be observed in photoemission experiments. Our method allows us to comprehensively unravel the surface-state spin structure driven by spin-orbit coupling at the ferromagnetic surface. This approach opens up opportunities to characterize the spin structure of ferromagnetic Rashba materials, especially where dedicated spin-resolved measurements remain challenging., This work was supported by Saint Petersburg State University (Grant No. ID 51126254) and the Russian Foundation for Basic Research (Grant No. 20-32-70127). We acknowledge financial support from the Spanish Ministry of Economy (No. MAT-2017-88374-P) and the German Research Foundation (DFG) through Grants No. LA655/20-1, No. KR3831/5-1, and Fermi-NEst. We acknowledge Diamond Light Source for access to beamline I05 (Proposals No. SI18844-1 and No. SI17761-1).

Angle-resolved photoemission spectroscopy (ARPES) has been used to study the electronic structure of InSe and CuIn5Se8 single crystals and determine the general patterns of its transformation after the introduction of copper. The main dispersion curves of valence bands in the studied multicomponent systems and the effective masses of majority carriers in CuIn5Se8 have been obtained. Joint theoretical and experimental research has allowed us to apply ARPES not only to single isolated states, but also to complex crystals with a large number of atoms in the unit cell (and, consequently, a large number of dispersion bands). It has been demonstrated that the neighborhoods of maxima and minima of dispersion curves E(k), which essentially define the set of experimental ARPES spectra, make the dominant contribution to the observed signal intensity.

Efficient control over the grain boundaries (GBs) is a vital aspect in optimizing the graphene growth conditions. A number of methods for visualization of GBs were developed for graphene grown on weakly interacting surfaces. Here, we utilize oxygen intercalation to reveal GBs and study their morphology for graphene strongly bound to the cobalt surface. We demonstrate that upon the intercalation of oxygen, GBs in polycrystalline graphene become easily detectable due to graphene cracking and selective oxidation of the substrate, thus giving a direct insight into the graphene micro- and nanostructure by means of different electron microscopy methods, including scanning electron microscopy, photoemission microscopy and low-energy electron microscopy.

A new method for synthesis of graphene-protected iron silicides has been tested, which consists in formation of graphene on Ni(111) followed by two-step intercalation of the system with Fe and Si. Characterization of the samples was performed in situ by low-energy electron diffraction, angular-resolved photoelectron spectroscopy, core-level photoelectron spectroscopy with synchrotron radiation and magnetic linear dichroism in photoemission of Fe 3p electrons. It is shown, that at 400 °C the intercalation of graphene/Ni(111) with iron occurs in a range up to 14 ML. The graphene layer strongly interacts with the topmost Fe atoms and stabilizes the fcc structure of the film. The in-plane ferromagnetic ordering of the film has a threshold nature and arises after the intercalation of 5 ML Fe due to the thickness-driven spin reorientation transition. Subsequent intercalation of graphene/Fe/Ni(111) with Si leads to the formation of the inhomogeneous system consisted of intercalated and nonintercalated areas. The intercalated islands coalesce at 2 ML Si when a Fe-Si solid solution covered with the Fe3Si surface silicide is formed. The Fe3Si silicide is ferromagnetic and has an ordered (√3 × √3)R30° structure. The graphene layer is weakly electronically coupled to the silicide phase keeping its remarkable properties ready for use.

We present a first-principles study of the ${\mathrm{GdRh}}_{2}{\mathrm{Si}}_{2}$(001) surface electronic structure. Two surfaces, Si- and Gd-terminated, are considered. The origin of the two-dimensional (2D) electronic states at both terminations is investigated by tracing the band structure evolution by going from individual Si, Rh, and Gd atomic layers to (non)stoichiometric ultrathin films and, finally, to thicker ${\mathrm{GdRh}}_{2}{\mathrm{Si}}_{2}$ slabs. We find the conic-like (Dirac-like) resonance state located in the vicinity of the $\overline{\mathrm{\ensuremath{\Gamma}}}$ point at the Si termination to form via the Tamm mechanism and explain the reasons for the differences in dispersion and energy position of the resonance states at the Si and Gd terminations. Then, we show how the butterfly-like dispersion of the Shockley state, residing in the bulk projected band gap near the $\overline{\mathrm{M}}$ point, appears due to the interaction of the bands localized in the surface and subsurface Gd-Si-Rh-Si blocks of the Si termination. Also, a giant sign-alternating atomic relaxation near both the Si- and Gd-terminated surfaces is revealed and its effect on the dispersion and energy position of the 2D states is discussed. In this way we shed light on the origin of the 2D states and explain their dispersion seen in angle-resolved photoemission spectroscopy experiments.

Application of the Luttinger theorem to the Kondo lattice YbRh2Si2 suggests that its large 4f-derived Fermi surface (FS) in the paramagnetic (PM) regime should be similar in shape and volume to that of the divalent local-moment antiferromagnet (AFM) EuRh2Si2 in its PM regime. Here we show by angle-resolved photoemission spectroscopy that paramagnetic EuRh2Si2 has a large FS essentially similar to the one seen in YbRh2Si2 down to 1 K. In EuRh2Si2 the onset of AFM order below 24.5 K induces an extensive fragmentation of the FS due to Brillouin zone folding, intersection and resulting hybridization of the Fermi-surface sheets. Our results on EuRh2Si2 indicate that the formation of the AFM state in YbRh2Si2 is very likely also connected with similar changes in the FS, which have to be taken into account in the controversial analysis and discussion of anomalies observed at the quantum critical point in this system., This work was supported by the German Research Foundation (DFG) (through grant Nos. GE 602/4-1, KR3831/5-1 and Fermi-NEst; GRK1621 and SFB1143), SaintPetersburg State University under Research Grant 15.61.202.2015, Spanish Ministry of Science and Innovation (Grant No. FIS2016-75862-P), and Tomsk State University Academic D.I. Mendeleev Fund Program (Grant No.8.1.01.2017). The SX-ARPES experiment was performed under Proposal Numbers 2016A3810 and 2018B3811 at SPring-8 BL23SU. The present work was financially supported by JSPS KAKENHI Grant Numbers 16H01084 (J-Physics) and 18K03553.

The implementation of future graphene-based electronics is essentially restricted by the absence of a band gap in the electronic structure of graphene. Options of how to create a band gap in a reproducible and processing compatible manner are very limited at the moment. A promising approach for the graphene band gap engineering is to introduce a large-scale sublattice asymmetry. Using photoelectron diffraction and spectroscopy we have demonstrated a selective incorporation of boron impurities into only one of the two graphene sublattices. We have shown that in the well-oriented graphene on the Co(0001) surface the carbon atoms occupy two nonequivalent positions with respect to the Co lattice, namely top and hollow sites. Boron impurities embedded into the graphene lattice preferably occupy the hollow sites due to a site-specific interaction with the Co pattern. Our theoretical calculations predict that such boron-doped graphene possesses a band gap that can be precisely controlled by the dopant concentration. B-graphene with doping asymmetry is, thus, a novel material, which is worth considering as a good candidate for electronic applications.

Ultrathin (∼2 nm) films of Co 2 FeSi ferromagnetic alloy were formed on silicon by solid-phase epitaxy and studied in situ . Experiments were carried out in an ultrahigh vacuum (UHV) using substrates of Si(1 1 1) single crystals covered with a 5 nm thick CaF 2 barrier layer. The elemental and phase composition as well as the magnetic properties of the synthesized films were analyzed by photoelectron spectroscopy using synchrotron radiation and by magnetic linear dichroism in photoemission of Fe 3 p and Co 3 p electrons. The study shows that the synthesis of the Co 2 FeSi ferromagnetic alloy occurs in the temperature range of 200–400 °C. At higher temperatures, the films become island-like and lose their ferromagnetic properties, as the CaF 2 barrier layer is unable to prevent a mass transfer between the film and the Si substrate, which violates the stoichiometry of the alloy.

The properties of atomically thin materials essentially depend on their structures, including impurities, defects and interfaces with underlying substrates. Thus, the detailed structural information is relevant for creation of 2D materials with desired properties. Here, we explore the capabilities of photoelectron diffraction and holography for structural analysis of atomically thin layers using as examples such systems as h-BN, graphene, and modified graphene with boron impurities. We show that for planar 2D crystals with commensurate interface to the substrate, it is possible to visualize the interface and impurities with high spatial resolution, and to distinguish possible non-equivalent structural units. Our approach applied to B-doped graphene on Ni(1 1 1) and Co(0 0 0 1) surfaces has allowed to reveal asymmetry of boron concentrations in the two carbon sublattices and established its dependence on the applied synthesis procedure and chosen substrate. The obtained results suggest that such approach can be widely applied for studies of various 2D systems, where the structures of interfaces and defects are of remarkable importance.

Embedding foreign atoms in graphene and interchanging the underlying substrate are proved to be efficient methods for manipulating the properties of graphene. Combining ARPES experiments with DFT calculations we show that boron-doped graphene (B-graphene) grown on a Co(0001) substrate by chemical vapor deposition (CVD) becomes hole doped and its Fermi surface near the K-point reveals strongly spin-polarized states. The latter stems from the spin-polarized mini Dirac cone that is an intrinsic two-dimensional feature of the graphene/Co(0001) interface and is formed by a mixture of C 2pz and Co 3d states. Since the CVD method allows the achievement of up to 20 at% of incorporated B atoms, this provides a certain flexibility for handling the spin-polarized properties of the system. We also show that the bonding of the B-graphene layer to the Co(0001) substrate can be released by intercalation of Li into the interface. This allows the exploration of the doping effect in detail. Finally, our ARPES data indicate a gap opening in the Dirac cone as a result of the highly unbalanced boron concentrations in the two graphene sublattices., We thank Helmholtz-Zentrum Berlin (HZB) for the allocation of synchrotron radiation beamtimes at the Russian-German and UE112-PGM1 beamlines. The work was financially supported by the joint project of the Russian Science Foundation (Grant No. 16-42-01093) and the DFG (Grant No. LA655-17/1).

The magnetic properties of rare earth compounds are usually well captured by assuming a fully localized $f$ shell and only considering the Hund's rule ground state multiplet split by a crystal electric field (CEF). Currently, the standard technique for probing CEF excitations in lanthanides is inelastic neutron scattering. Here we show that with the recent leap in energy resolution, resonant inelastic soft x-ray scattering (RIXS) has become an attractive alternative for looking at CEF excitations. This has been used for studying the CEF scheme in ${\mathrm{CeRh}}_{2}{\mathrm{Si}}_{2}$, a system that has been investigated intensely for more than two decades now but for which no consensus has been reached yet as to its CEF scheme. Using high energy resolution of about 30 meV as well as polarization analysis in the scattered beam, both features that have become available only very recently in RIXS, allowed us to find a unique CEF description for ${\mathrm{CeRh}}_{2}{\mathrm{Si}}_{2}$. The result agrees well with previous inelastic neutron scattering and magnetic susceptibility studies. Due to its strong resonant character, RIXS is applicable to very small samples, presents very high cross sections for all lanthanides, and further benefits from the very weak coupling to phonon excitations. The foreseeable further progress in energy resolution will make this technique increasingly attractive for the investigation of the CEF scheme in lanthanides.

The magnetic properties of rare earth compounds are usually well captured by assuming a fully localized f shell and only considering the Hund's rule ground state multiplet split by a crystal electric field (CEF). Currently, the standard technique for probing CEF excitations in lanthanides is inelastic neutron scattering. Here we show that with the recent leap in energy resolution, resonant inelastic soft x-ray scattering (RIXS) has become an attractive alternative for looking at CEF excitations. This has been used for studying the CEF scheme in CeRh2Si2, a system that has been investigated intensely for more than two decades now but for which no consensus has been reached yet as to its CEF scheme. Using high energy resolution of about 30 meV as well as polarization analysis in the scattered beam, both features that have become available only very recently in RIXS, allowed us to find a unique CEF description for CeRh2Si2. The result agrees well with previous inelastic neutron scattering and magnetic susceptibility studies. Due to its strong resonant character, RIXS is applicable to very small samples, presents very high cross sections for all lanthanides, and further benefits from the very weak coupling to phonon excitations. The foreseeable further progress in energy resolution will make this technique increasingly attractive for the investigation of the CEF scheme in lanthanides., This work was supported by the German Research Foundation (DFG) through Grant Nos. GE 602/4-1, KR 3831/5-1 and Fermi-NEst

Using photoelectron diffraction and spectroscopy, we explore the structural and electronic properties of the hexagonal boron nitride (h-BN) monolayer epitaxially grown on the Co(0001) surface. Perfect matching of the lattice parameters allows formation of a well-defined interface where the B atoms occupy the hollow sites while the N atoms are located above the Co atoms. The corrugation of the h-BN monolayer and its distance from the substrate were determined by means of R-factor analysis. The obtained results are in perfect agreement with the density functional theory (DFT) predictions. The electronic structure of the interface is characterized by a significant mixing of the h-BN and Co states. Such hybridized states appear in the h-BN band gap. This allows to obtain atomically resolved scanning tunneling microscopy (STM) images from the formally insulating 2D material being in contact with ferromagnetic metal. The STM images reveal mainly the nitrogen sublattice due to a dominating contribution of nitrogen orbitals to the electronic states at the Fermi level. We believe that the high quality, well-defined structure and interesting electronic properties make the h-BN/Co(0001) interface suitable for spintronic applications., L.V.Ya. acknowledges the RSF (Grant No. 16-42-01093). A.V.T., V.O.S., K.A.B., O.Yu.V., and D.Yu.U. acknowledge St. Petersburg State University for research Grant No. 11.65.42.2017. M.V.K. and I.I.O. acknowledge the RFBR (Grant No. 16-29-06410). C.L. acknowledges the DFG (Grant Nos. LA655-17/1 and LA655-19/1).

The structural and electronic properties of hexagonal boron nitride (hBN) grown on stepped Ni surfaces are systematically investigated using a cylindrical Ni crystal as a tunable substrate. Our experiments reveal homogeneous hBN monolayer coating of the entire Ni curved surface, which in turn undergoes an overall faceting. The faceted system is defined by step-free hBN/Ni(1 1 1) terraces alternating with strongly tilted hBN/Ni(1 1 5) or hBN/Ni(1 1 0) nanostripes, depending on whether we have A-type or B-type vicinal surfaces, respectively. Such deep substrate self-organization is explained by both the rigidity of the hBN lattice and the lack of registry with Ni crystal planes in the vicinity of the (1 1 1) surface. The analysis of the electronic properties by photoemission and absorption spectroscopies reveal a weaker hBN/Ni interaction in (1 1 0)- and (1 1 5)-oriented facets, as well as an upward shift of the valence band with respect to the band position at the hBN/Ni(1 1 1) terrace., We acknowledge financial support from the Deutsches Forschungsgemein chaft DFG (Grants LA655-17/1 and LA655-19/1), the Spanish Ministry of Economy (Grants MAT-2016-78293-C6, MAT-2017-88374-P), the Basque Government (Grant IT-1255-19), the Helmholtz-Zentrum Berlin für Materialien und Energie for support within the bilateral RussianGerman Laboratory program as well as from the joint project of the Russian Science Foundation (project 16-42-01093) and DFG (Grant No. LA655-17/1). DYuU acknowledges St. Petersburg State University for research Grant No. 11.65.42.2017 and Russian Foundation for Basic Research RFBR (Project No. 17-02-00427).

Using angle-resolved photoemission spectroscopy (ARPES), we study the electronic structure and electron-phonon coupling in a Li-doped graphene monolayer decoupled from the Co(0001) substrate by intercalation of silicon. Based on the photoelectron diffraction measurements, we disclose the structural properties of the Si/Co interface. Our density functional theory calculations demonstrate that in the studied Li/graphene/Si/Co system the magnetism of Co substrate induces notable magnetic moments on Li and Si atoms. At the same time graphene remains almost nonmagnetic and clamped between two magnetically active atomic layers with antiparallel magnetizations. ARPES maps of the graphene Fermi surface reveal strong electron doping, which may lead to superconductivity mediated by electron-phonon coupling (EPC). Analysis of the spectral function of photoelectrons reveals apparent anisotropy of EPC in the k space. These properties make the studied system tempting for studying the relation between superconductivity and magnetism in two-dimensional materials., D.Yu.U., D.V.V., and A.V.F. acknowledge SPbU for research Grant No. 11.65.42.2017 and RFBR (Grant No. 17-02-00427). D.Yu.U., I.I.O., and M.V.K. acknowledge RFBR (Grant No. 16-29-06410). C.L. acknowledges DFG (Grant No. LA655-17/1). A.G. and A.V.F. acknowledge ERC Grant No. 648589 “SUPER-2D” and funding from DFG project CRC 1238 (project A1) and DFG project GR 3708/2-1. We acknowledge Helmholtz-Zentrum Berlin für Materialien und Energie for support within the bilateral Russian-German Laboratory program.

Strong spin-orbit coupling (SOC) in combination with a lack of inversion symmetry and exchange magnetic interaction proves to be a sophisticated instrument allowing efficient control of the spin orientation, energy and trajectories of two-dimensional (2D) electrons and holes trapped at surfaces or interfaces. Exploiting Kondo-related phenomena and crystal-electric-field effects at reduced dimensionalities opens new opportunities to handle their spin-dependent properties offering novel functionalities. We consider here a 2D Kondo lattice represented by a Si-Ir-Si-Yb (SISY) surface block of the heavy-fermion material YbIr2Si2. We show that the Kondo interaction with 4f moments allows finely tuning the group velocities of the strongly spin-polarized carriers in 2D itinerant states of this noncentrosymmetric system. To unveil the peculiarities of this interaction, we used angle-resolved photoemission measurements complemented by first-principles calculations. We established that the strong SOC of the Ir atoms induces spin polarization of the 2D states in SISY block, while the 2D lattice of Yb 4f moments acts as a source for coherent f−d interplay. The strong SOC and lack of inversion symmetry turn out to lead not only to the anticipated Rashba-like splitting of the 2D states, but also to spin splitting of the 4f Kramers doublets. They couple temperature-dependently to the spin-polarized 2D states and thereby guide the properties of the latter., This work was supported by the German Research Foundation (DFG; Grants No. GRK1621, No. KR3831/5-1, No. GE 602/4-1 Fermi Nest and No. SFB1143) as well as Research Grant No. 15.61.202.2015 of Saint-Petersburg State University. We also acknowledge the funding by the Basque Departamento de Educacion, UPV/EHU (Grant No. IT-756-13), the Spanish Ministry of Economy, Industry and Competitiveness MINEICO (Grants No. FIS2016-75862-P and No. FIS2016-76617-P), and Tomsk State University competitiveness improvement programme (project No. 8.1.01.2017)

This work presents an extreme biomimetics route for the creation of nanostructured biocomposites utilizing a chitinous template of poriferan origin. The specific thermal stability of the nanostructured chitinous template allowed for the formation under hydrothermal conditions of a novel germanium oxide-chitin composite with a defined nanoscale structure. Using a variety of analytical techniques (FTIR, Raman, energy dispersive X-ray (EDX), near-edge X-ray absorption fine structure (NEXAFS), and photoluminescence (PL) spectroscopy, EDS-mapping, selected area for the electron diffraction pattern (SAEDP), and transmission electron microscopy (TEM)), we showed that this bioorganic scaffold induces the growth of GeO2 nanocrystals with a narrow (150–300 nm) size distribution and predominantly hexagonal phase, demonstrating the chitin template’s control over the crystal morphology. The formed GeO2–chitin composite showed several specific physical properties, such as a striking enhancement in photoluminescence exceeding values previously reported in GeO2-based biomaterials. These data demonstrate the potential of extreme biomimetics for developing new-generation nanostructured materials.

The intercalation of silicon under graphene on the Co(0001) surface, which is accompanied by the formation of a silicon solid solution in cobalt and by the formation of a surface crystalline Co2Si phase, has been investigated using photoelectron spectroscopy. It has been shown that the formation of cobalt silicide leads to a substantial weakening of the hybridization of electronic states of graphene and cobalt and to the recovery of the Dirac spectrum of electronic states of graphene near the Fermi level. This has made it possible to investigate the electron doping of graphene on the cobalt silicide substrate upon deposition of lithium on its surface. It has been found that doping with lithium leads to a significant charge transfer onto graphene, and the electron concentration reaches 3.1 × 1014 cm−2. Moreover, the specific form of the Fermi surface creates favorable conditions for the enhancement of the electron-phonon coupling. As a result, the formed system can be considered as a candidate for the creation of superconductivity in single-layer graphene.

Analyzing temperature dependent photoemission (PE) data of the ferromagnetic Kondo-lattice (KL) system YbNiSn in the light of the periodic Anderson model (PAM) we show that the KL behavior is not limited to temperatures below a temperature ¯¯¯TK, defined empirically from resistivity and specific heat measurements. As characteristic for weakly hybridized Ce and Yb systems, the PE spectra reveal a 4f-derived Fermi level peak, which reflects contributions from the Kondo resonance and its crystal electric field (CEF) satellites. In YbNiSn this peak has an unusual temperature dependence: With decreasing temperature a steady linear increase of intensity is observed which extends over a large interval ranging from 100 K down to 1 K without showing any peculiarities in the region of ¯¯¯TK∼TC=5.6 K. In the light of the single-impurity Anderson model (SIAM) this intensity variation reflects a linear increase of 4f occupancy with decreasing temperature, indicating an onset of Kondo screening at temperatures above 100 K. Within the PAM this phenomenon could be described by a non-Fermi-liquid-like T- linear damping of the self-energy which accounts phenomenologically for the feedback from the closely spaced CEF states., This work was supported by the German Research Foundation (DFG; Grants No. VY64/1-3, No. GE602/2-1, No. GRK1621, and SFB1143) and by Research Grant No. 15.61.202.2015 of Saint Petersburg State University. D.A.S. and A.D.H. acknowledge support from EPSRC Grant No. EP/J00099X/1.

Using resonant angle-resolved photoemission spectroscopy and electron band-structure calculations, we explore the electronic structure and properties of Sm atoms at the surface and in the bulk of the antiferromagnet SmRh2Si2. We show that the Sm atoms reveal weak mixed-valent behavior both in the bulk and at the surface. Although trivalent 4f emission strongly dominates, a small divalent 4f signal near the Fermi energy can be clearly resolved for surface and bulk Sm atoms. This behavior is quite different to most other Sm-based materials which typically experience a surface valence transition to a divalent state of Sm atoms at the surface. This phenomenon is explained in analogy to the isostructural Ce compound, where strong 4f hybridization stabilizes mixed-valent ground state both in the bulk and at the surface, and which were described in the light of the single-impurity Anderson model. Implications for other RERh2Si2 (RE = rare-earth elements) compounds are discussed.

The paper reports the relationship between single-walled carbon nanotube (SWNT) doping and capsulate crystal structure in RbxAg1−xI@SWNT composites. The structures of one dimensional (1D) RbI, AgI and RbAg4I5 crystals inside single-walled carbon nanotubes were established by high-resolution transmission electron microscopy (HRTEM) and high-resolution scanning transmission electron microscopy (HAADF HRSTEM), and confirmed by image simulation. Opposite to one-dimensional RbI and AgI, inheriting the structure of bulk analogues, 1D RbAg4I5 forms a new phase within a confined space of the SWNT channel, which differs from the bulk RbAg4I5 structure and can be described by a deformed cubic 1D lattice. X-ray absorption, XPS, optical absorption and Raman spectroscopies were used for comprehensive study of the composites' electronic structures. The study reveals the donor behavior of RbI capsulate and the acceptor behavior of RbAg4I5 and AgI. Quantification of doping levels indicated the prevalence of the effect of the chemical composition of the capsulate on the overall doping efficiency, while a structural effect is mostly prominent in potential distribution on nanotube walls and partial charges on SWNT atoms., This work was supported by the Helmholtz Zentrum Berlin für Materialien und Energie within a bilateral Russian-German Laboratory program. The authors express gratitude to Orekhov A. S. for help with the STEM image simulation. This work was performed using the equipment of the Shared Research Centre FSRC “Crystallography and Photonics” RAS and was supported by the Russian Ministry of Education and Science.

Finding ways to create and control the spin-dependent properties of two-dimensional electron states (2DESs) is a major challenge for the elaboration of novel spin-based devices. Spin–orbit and exchange–magnetic interactions (SOI and EMI) are two fundamental mechanisms that enable access to the tunability of spin-dependent properties of carriers. The silicon surface of HoRh2Si2 appears to be a unique model system, where concurrent SOI and EMI can be visualized and controlled by varying the temperature. The beauty and simplicity of this system lie in the 4f moments, which act as a multiple tuning instrument on the 2DESs, as the 4f projections parallel and perpendicular to the surface order at essentially different temperatures. Here we show that the SOI locks the spins of the 2DESs exclusively in the surface plane when the 4f moments are disordered: the Rashba-Bychkov effect. When the temperature is gradually lowered and the system experiences magnetic order, the rising EMI progressively competes with the SOI leading to a fundamental change in the spin-dependent properties of the 2DESs. The spins rotate and reorient toward the out-of-plane Ho 4f moments. Our findings show that the direction of the spins and the spin-splitting of the two-dimensional electrons at the surface can be manipulated in a controlled way by using only one parameter: the temperature., This work was supported by the German Research Foundation (DFG) (Grant Nos. VY64/1-3, GE602/2-1, GRK1621, and SFB1143) as well as by Research Grant No. 15.61.202.2015 of Saint Petersburg State University. We acknowledge Diamond Light Source for beamtime on the beamline I05 under proposal SI11512. The authors acknowledge experimental support from the SIS beamline at Swiss Light Source. The support by the Tomsk State University Academic D.I. Mendeleev Fund Program in 2015 (research grant N 8.1.05.2015), the University of the Basque Country (Grants Nos. GIC07IT36607 and Grant No. IT-756-13), and the Spanish Ministry of Science and Innovation (Grant Nos. FIS2013-48286-C02-02-P and FIS2013-48286-C02-01-P) is also acknowledged.

Fluorinated graphite intercalation compounds (FGICs) with acetonitrile C2Fx · yCH3CN (x = 0.92, 0.69, and 0.49) have been synthesized using a gaseous mixture of BrF3 and Br2 at room temperature and subsequent replacement of the reaction medium components on acetonitrile by isopiestic method. The change in functional composition and electronic structure of FGICs under annealing at 250–260 °C was studied by infrared, X-ray photoelectron, and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) methods. Analysis of the data revealed interaction of acetonitrile with a C2Fx matrix. The X-ray spectra detected formation of new nitrogen species attributed to two-coordinated and mono hydrogenated three-coordinated atoms. Mechanism of nitrogen incorporation in the fluorinated graphene layers was proposed. Schematic structure of graphite fluoride C2Fx intercalated with acetonitrile and NEXAFS N K-edge spectrum of C2F0.69 · 0.137CH3CN before and after annealing at 250 °C.

Copper containing bismuth titanates with pyrochlore type structure were obtained by ceramic procedure over a wide range of compositions. The results of measurement of pycnometric density of the pyrochlores and of X-ray powder diffraction structure refinement point to the preference for copper atoms to occupy the Bi 3 + -sites. TGA study of a series of synthesized compounds indicates a reversible reduction of the copper (2) to copper (1). The NEXAFS Cu2p spectra of bismuth copper titanate pyrochlores point to copper being mainly in the oxidation state + 2 in these solid solutions. Electric properties were studied for single phase pyrochlores based on bismuth titanates. The results of investigations show the presence of oxygen ionic conductivity in these samples.

Many propositions have been already put forth for the practical use of N-graphene in various devices, such as batteries, sensors, ultracapacitors, and next generation electronics. However, the chemistry of nitrogen imperfections in this material still remains an enigma. Here we demonstrate a method to handle N-impurities in graphene, which allows efficient conversion of pyridinic N to graphitic N and therefore precise tuning of the charge carrier concentration. By applying photoemission spectroscopy and density functional calculations, we show that the electron doping effect of graphitic N is strongly suppressed by pyridinic N. As the latter is converted into the graphitic configuration, the efficiency of doping rises up to half of electron charge per N atom.

Recently, a new dual plasma-process to produce non noble metal catalysts for the oxygen reduction in proton exchange membrane fuel cells has been developed and catalytically active cobalt–polypyrrole-films have been produced. This paper shows a modification to this process, so that iron–polypyrrole is formed. The magnetron power as well as the process gases were varied. The structure of the compounds was then analyzed by energy-dispersive X-ray spectroscopy, X-ray diffraction, near edge X-ray absorption fine structure and extended X-ray absorption fine structure. It is shown that the oxidation of the compounds is suppressed when hydrogen or nitrogen is added to the process. Furthermore, cyclic voltammetry and rotating ring-disk electrode measurements were done to determine the electrochemical properties of the films. Only films produced in hydrogen or nitrogen containing gases show catalytic activity and it can be seen that the four-electron reduction mechanism is dominant.

The recently discovered “rods-in-belt” supramolecular complexes with Au Cu or Au Ag cluster cores exhibit self-assembly behavior, have a very unusual structural motif, and what is most important, show remarkable light emitting properties. The electronic and photophysical characteristics of these unique objects can be relatively easy tuned by modifying the ligand (alkynyl and phosphine) environment. Because of these properties the “rods-in-belt” supramolecules could serve as building blocks for next generation electronics, and in particular, for light-emitting devices and in bioimaging applications. Herein, we report a comprehensive characterization of the electronic structure of two families of alkynyl-diphosphine supramolecular complexes with the heterometallic Au Cu and Au Ag cores. Using X-ray photoemission and absorption spectroscopy we disentangled the structure of their occupied and unoccupied electronic states close to the Fermi level. The results obtained suggest that the major contribution to the highest occupied molecular orbitals is made by the triple bonded carbons hosted in the dialkynyl-gold “rods” and the copper (silver) atoms from the central cluster core of the heterometallic Au Cu (Au Ag) molecules. The lowest unoccupied molecular orbitals are located on the carbon skeleton of the complexes and include π*-C C and π*-C C aromatic orbitals. The onset of the valence band in the Au Ag systems starts at about 0.3 eV lower than that in the Au Cu complexes, implying a slightly larger energy gap for the silver-based systems. It was also established that with increasing size of the complexes, the molecule becomes more and more sensitive to X-ray damage effects.

The crystalline and electronic structure of nitrogen-doped graphene (N-graphene) has been studied by photoelectron spectroscopy and scanning tunneling microscopy. Synthesis of N-graphene from triazine molecules on Ni(111) surface results in incorporation into graphene of nitrogen atoms primarily in the pyridinic configuration. It has been found that inclusions of nitrogen enhance significantly thermal stability of graphene on nickel. An analysis of the electronic structure of N-graphene intercalated by gold atoms has revealed that the pyridinic nitrogen culminates in weak p-type doping, in full agreement with theoretical predictions. Subsequent thermal treatment makes possible conversion of the major part of nitrogen atoms into the substitutional configuration, which involves n-type doping. It has been shown that the crystalline structure of the N graphene thus obtained reveals local distortions presumably caused by inhomogeneous distribution of impurities in the layer. The results obtained have demonstrated a promising application potential of this approach for development of electronic devices based on graphene with controllable type of conduction and carrier concentration.

We present a detailed study on the physical properties of single crystals of the Eu3+ intermetallic EuCo2Si2. The Eu valence was confirmed by X-ray absorption. At low temperatures, the anisotropic susceptibility can be explained by a Eu3+ Van Vleck contribution with a crystal field parameter , but at high temperatures the data exceed the Van Vleck values significantly. This excess susceptibility is possibly related to the magnetic exchange between the excited Eu multiplets and the conduction band. A γ of 9.6 mJ K−2 mol and a Debye temperature of 322 K were estimated from the low temperature specific heat data. The compound does not undergo any phase transition in the temperature range 2–300 K.

The hybridization between localized 4f electrons and itinerant electrons in rare-earth-based materials gives rise to their exotic properties like valence fluctuations, Kondo behaviour, heavy-fermions, or unconventional superconductivity. Here we present an angle-resolved photoemission spectroscopy (ARPES) study of the Kondo lattice antiferromagnet CeRh2Si2, where the surface and bulk Ce-4f spectral responses were clearly resolved. The pronounced 4f 0 peak seen for the Ce terminated surface gets strongly suppressed in the bulk Ce-4f spectra taken from a Si-terminated crystal due to much larger f-d hybridization. Most interestingly, the bulk Ce-4f spectra reveal a fine structure near the Fermi edge reflecting the crystal electric field splitting of the bulk magnetic 4f 15/2 state. This structure presents a clear dispersion upon crossing valence states, providing direct evidence of f-d hybridization. Our findings give precise insight into f-d hybridization penomena and highlight their importance in the antiferromagnetic phases of Kondo lattices., In rare-earth intermetallics, interaction between localized 4f electrons and itinerant electrons can result in exotic states of matter. Here, the authors use photoemission spectroscopy to reveal and study this interaction in the bulk and at the surface of the Kondo lattice antiferromagnet CeRh2Si2.

International audience; Diatoms are considered unicellular eukaryotic organisms exclusively depositing biogenic silica. Heretofore there has been no report of calcification by these algae. Here it is shown that calcium carbonate within the stalks of Didymosphenia geminata, a nuisance species that has prolifically colonized streams and rivers globally, is biogenic in origin and occurs as a network of calcite nanofibers. The nanofibrous framework in the mineralized polysaccharide matrix imparts mechanical support to the stalks, providing stability in variable flow conditions. The results demonstrate that D. geminata possesses cellular and periplasmic carbonic‐anhydrases that contribute to carbon fixation and biomineralization, respectively. The activity of external carbonic‐anhydrase was more than 50% of the total activity, which points to its role in anchoring this bioeroding diatom on hard surfaces. The first evidence of multiphase biomineralization by diatoms that deposit both biogenic silica and crystalline biogenic calcite which are imparting distinct functional advantage to the organism is provided.

The potential of resonant inelastic soft x-ray scattering to measure $4f$ crystal electric-field excitation spectra in Ce Kondo lattices has been examined. Spectra have been obtained for several Ce systems and show a well-defined structure determined by crystal-field, spin-orbit, and charge-transfer excitations only. The spectral shapes of the excitation spectra can be well understood in the framework of atomic multiplet calculations. For ${\mathrm{CeCu}}_{2}{\mathrm{Si}}_{2}$ we found notable disagreement between the inelastic x-ray-scattering spectra and theoretical calculations when using the crystal-field scheme proposed from inelastic neutron scattering. Modified sets of crystal-field parameters yield better agreement. Our results also show that, with the very recent improvements of soft x-ray spectrometers in resolution to below 30 meV at the Ce ${M}_{4,5}$ edges, resonant inelastic x-ray scattering could be an ideal tool to determine the crystal-field scheme in Ce Kondo lattices and other rare-earth compounds.

Manganese-containing bismuth titanate solid solutions with a pyrochlore-type crystal structure were obtained by the ceramic technique over a wide range of compositions. The NEXAFS (near-edge X-ray absorption fine structure) spectra of Mn2p-absorption in bismuth manganese titanate pyrochlores point to manganese being mainly in the oxidation state + 2 in these solid solutions. The Mn-rich bismuth titanate pyrochlores showed a superposition of antiferro- (long-order) and ferromagnetic (short-order) behavior. The results of impedance investigations show the electron–ionic conductivity in these samples.