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Tardigrades can cope with adverse environmental conditions by turning into anhydrobiotes with a characteristic tun shape. Tun formation is an essential morphological adaptation for tardigrade entry into the anhydrobiotic state. The tun cell structure and ultrastructure have rarely been explored in tardigrades in general and never in Hypsibius exemplaris. We used transmission electron microscopy to compare cellular organization and ultrastructures between hydrated and anhydrobiotic H. exemplaris. Despite a globally similar cell organelle structure and a number of cells not significantly different between hydrated and desiccated tardigrades, reductions in the sizes of both cells and mitochondria were detected in dehydrated animals. Moreover, in anhydrobiotes, secretory active cells with a dense endoplasmic reticulum network were observed. Interestingly, these anhydrobiote-specific cells are in a close relationship with a specific extracellular structure surrounding each cell. It is possible that this rampart-like extracellular structure resulted from the accumulation of anhydrobiotic-specific material to protect the cells. Interestingly, after five hours of rehydration, the number of secretory cells decreased, and the specific extracellular structure began to disappear. Twenty-four hours after the beginning of rehydration, the cellular structure and ultrastructure were comparable to those observed in hydrated tardigrades.

Angle-resolved photoemission spectromicroscopy on IrTe2 reveals evolution of mesoscopic striped domains across its first order phase transition at about 280 K. The striped texture of the domains is characterized by a herringbone arrangement of the electronic anisotropy axes. Under further cooling down to 47 K, the striped domains evolve into trijunction domains with the electronic anisotropy in three directions. Each domain harbors quasi one-dimensional surface bands forming Fermi arcs with peculiar spin polarization. The Fermi arc corresponds to an edge state of the two-dimensional bulk electronic states truncated at the surface, indicating an interesting interplay between the symmetry breaking and the surface electronic states., Comment: 11 pages + 5 figures

The local structure of La(Fe1-xMnx)AsO, showing suppression of long-range magnetic order by Mn-substitution, has been studied. Extended X-ray absorption fine structure (EXAFS) measurements at As K-edge and Fe K-edge are used to probe the atomic correlations in the FeAs-layer. We have found that both Fe-As and Fe-Fe bondlengths tend to increase with increasing Mn concentration. The associated mean square relative displacements (MSRD) reveal a gradual increase indicating increased local disorder in the FeAs-layer with Mn content. The results reveal that the FeAs-layer thickness, measured by the As-height (hAs) from the Fe-Fe plane, is correlated with the Neel temperature. Furthermore, Fe Kβ X-ray emission spectroscopy (XES) shows a sharp increase in the Fe local magnetic moment with Mn substitution. The importance of the FeAs layer thickness in describing magnetic correlations in La(Fe1−xMnx)AsO is discussed.

We have investigated the electronic structure evolution with F doping in $\mathrm{Pr}{\mathrm{O}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}\mathrm{Bi}{\mathrm{S}}_{2}$ ($x=0.0,0.3,0.5$) by means of angle-resolved photoemission spectroscopy. Undoped $\mathrm{Pr}\mathrm{O}\mathrm{Bi}{\mathrm{S}}_{2}$ exhibits Fermi surface (FS) pockets around the $X$ point which can be associated with electron doping due to the ${\mathrm{Pr}}^{3+}/{\mathrm{Pr}}^{4+}$ mixed valence. At $x=0.3$, the FS pockets are expanded, and their area is almost consistent with the F doping level. Interestingly, horizontal segments facing each other in the rectangular FS pockets lose their spectral weight. The partial suppression of the FS pockets suggests possible anisotropic charge fluctuations around $x=0.3$. At $x=0.5$, the FS area is much smaller than the expected value as commonly observed for $\mathrm{Ce}{\mathrm{O}}_{0.5}{\mathrm{F}}_{0.5}\mathrm{Bi}{\mathrm{S}}_{2}$ and $\mathrm{Nd}{\mathrm{O}}_{0.5}{\mathrm{F}}_{0.5}\mathrm{Bi}{\mathrm{S}}_{2}$. In addition, the highly depleted spectral weight at the FS pockets would be consistent with evident charge fluctuations driven by atomic disorder in the $\mathrm{Bi}{\mathrm{S}}_{2}$ network.

Recently, ammonia-thermal reaction has been used for molecular intercalation in layered FeSe, resulting a new Lix(NH3)yFe2Se2 superconductor with Tc ~ 45 K. Here, we have used temperature dependent extended x-ray absorption fine structure (EXAFS) to investigate local atomic displacements in single crystals of this new superconductor. Using polarized EXAFS at Fe K-edge we have obtained direct information on the local Fe-Se and Fe-Fe bondlengths and corresponding mean square relative displacements (MSRD). We find that the Se-height in the intercalated system is lower than the one in the binary FeSe, suggesting compressed FeSe4 tetrahedron in the title system. Incidentally, there is hardly any effect of the intercalation on the bondlengths characteristics, revealed by the Einstein temperatures, that are similar to those found in the binary FeSe. Therefore, the molecular intercalation induces an effective compression and decouples the FeSe slabs. Furthermore, the results reveal an anomalous change in the atomic correlations across Tc, appearing as a clear decrease in the MSRD, indicating hardening of the local lattice mode. Similar response of the local lattice has been found in other families of superconductors, e.g., A15-type and cuprates superconductors. This observation suggests that local atomic correlations should have some direct correlation with the superconductivity.

Temperature-dependent Fe K-edge extended X-ray absorption fine structure (EXAFS) and Fe Kβ X-ray emission spectroscopy (XES) measurements are used to study the local structure and local Fe magnetic...

We report time- and angle-resolved photoemission spectroscopy on SnSe which currently attracts great interest due to its extremely high thermoelectric performance. Laser-assisted photoemission signals are observed within $\pm$20 fs of the pump pulse arrival. Around 30-50 fs after the photoexcitation, the conduction band minima are not populated by the photoexcited electrons while the valence bands are considerably broadened. In going from 90 fs to 550 fs after the photoexcitation, the photoexcited carriers are decayed into the multiple conduction band minima. The observed conduction bands are consistent with the band structure calculations. The multiple conduction minima suggest possibility of high and anisotropic thermoelectric performance of n-type SnSe single crystal if it is realized., Comment: 5 pages, 4 figures

We report the tilt sensitivity reached by the ARCHIMEDES tiltmeter in the 2–20 Hz frequency region, where seismic noise is expected to give an important limitation to the sensitivity in the next future Gravitational Waves detection, particularly through Newtonian noise. The tilt noise level $$\tilde{\theta }(f)$$ θ ~ ( f ) is about $$10^{-12} \mathrm{rad}/\sqrt{\mathrm{Hz}}$$ 10 - 12 rad / Hz in most of the band, reaching the minimum of $$\tilde{\theta } = 7\cdot 10^{-13} \mathrm{rad}/\sqrt{\mathrm{Hz}}$$ θ ~ = 7 · 10 - 13 rad / Hz around 9 Hz. The tiltmeter is a beam balance with a 0.5 m suspended arm and interferometric optical readout, working in closed loop. The results have been obtained by a direct measurement of the ground tilt at the Sos Enattos site (Sardinia, Italy). This sensitivity is a requirement to use the tiltmeter as part of an effective Newtonian noise reduction system for present Gravitational Waves detectors, and also confirms that Sos Enattos is among the quietest sites in the world, suitable to host the third-generation Gravitational Waves detector Einstein Telescope.

We have investigated the electronic structure of protect annealed Pr1.3−xLa0.7CexCuO4 (x = 0.05) with small superconducting volume fraction by means of angle-resolved photoemission spectroscopy (AR...

Many technological applications demand large amount of nanoparticles with well-defined properties, which is feasible only by using large-scale production methods. In this framework, we have performed structural and local geometric investigations of cobalt oxide nanoparticles synthesized by high temperature arc plasma route in helium and in air atmosphere with different arc currents, a competitive and low cost technological approach to synthesize large quantity of different types of nanoparticles. The complex scenario of phase fraction, shape, size distribution and hysteresis loop features of high temperature arc plasma synthesis of nanoparticles can be determined by the arc current and the selected gas. X-ray diffraction patterns reveal a multicomponent phase formation containing cubic cobaltous oxide (CoO), cobaltic oxide (Co3O4) and metallic cobalt phases. The synthesis of different phases is confirmed by x-ray absorption spectroscopy measurements at the Co K-edge. Both extended x-ray absorption fine structure and x-ray absorption near edge structure analyses show the presence of metallic nanoparticles in He ambient at high arc current. Moreover, high-resolution transmission electron microscopy images and magnetic hysteresis loop measurements show that the mean particle size increases and the coercivity decreases with increasing arc current in air ambient due to the intense particle–particle interaction. At variance, in He ambient synthesized samples due to the high quenching rate and the high thermal conductivity, a multi-domain formation in which the nanoparticles’ crystalline fraction decreases and a fluctuating coercivity due to core–shell structure is observed.

The ${\mathrm{BiS}}_{2}$-based layered materials are characterized by a highly susceptible physical state, revealing a large response to external conditions. A particular case is the ${\mathrm{EuFBiS}}_{2}$ compound, showing a superconducting transition temperature ${T}_{c}\ensuremath{\sim}0.3$ K at ambient pressure. Upon increasing external pressure, ${T}_{c}$ goes through a large amplification, accompanied by a structural phase transition (SPT) from tetragonal to monoclinic symmetry. Here, we use a combination of Eu ${\phantom{\rule{4pt}{0ex}}L}_{3}$ - edge x-ray absorption spectroscopy and synchrotron x-ray diffraction to unveil the evolution of the Eu valence and lattice symmetry under high pressure. We find that the average Eu valence increases gradually with pressure, exhibiting a pressure plateau near the SPT, at which the ${T}_{c}$ increases sharply. Since in ${\mathrm{EuFBiS}}_{2}$ the charge carriers are introduced via self-doping induced by the mixed valence of the Eu ions, our findings clearly indicate that the role of the charge doping is marginal in the ${T}_{c}$ enhancement. On the other hand, the structural distortions, taking place at the SPT, play a central role in enhancing the superconducting properties of the ${\mathrm{EuFBiS}}_{2}$ system.

Physical review / B 101(2), 020508 (2020). doi:10.1103/PhysRevB.101.020508, The coexistence of phases, characterized by different electronic degrees of freedom, commonly occurs in layered superconductors. Among them, alkaline intercalated chalcogenides are model systems showing the microscale coexistence of paramagnetic (PAR) and antiferromagnetic (AFM) phases, however, the temporal behavior of different phases is still unknown. Here, we report a visualization of the atomic motion in the granular phase of KxFe2−ySe2 using x-ray photon correlation spectroscopy. Unlike the PAR phase, the AFM texture reveals an intermittent dynamics with avalanches as in martensites. When cooled down across the superconducting transition temperature Tc, the AFM phase goes through an anomalous slowing behavior, suggesting a direct relationship between the atomic motions in the AFM phase and the superconductivity. In addition to providing compelling evidence of avalanchelike dynamics in a layered superconductor, the results provide a basis for different theoretical models to describe the quantum states in inhomogeneous solids., Published by Inst., Woodbury, NY

We investigate the metal to nonmagnetic insulator (MI) transition of MnP-type Ru pnictide RuP using hard x-ray and ultraviolet photoemission spectroscopies. The spectral weight at ${E}_{\mathrm{F}}$ is suppressed below the MI transition temperature ${T}_{\mathrm{MI}}$, while there is no appreciable change across the pseudogap temperature ${T}_{\mathrm{PG}}$. The estimated energy scale of the gap is $\ensuremath{\sim}110$ meV, which is in good correspondence to the spin gap opening observed in the previous NMR study. According to the band structure calculation, the density of states at ${E}_{\mathrm{F}}$ mainly originates from narrow bands of the Ru $4{d}_{xy}$ orbitals. Our results suggest that the fourfold-degenerate Ru $4{d}_{xy}$ orbitals are deeply related to the MI transition. Based on the photoemission results and the band structure calculation, we argue the possible origin of the MI transition for polycrystalline RuP.

We have investigated electronic structure evolution by cation substitution in ${\mathrm{Ba}}_{3\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{Nb}}_{5}{\mathrm{O}}_{15}$ by means of hard x-ray photoemission spectroscopy. Localization of Nb $4d$ electrons manifests as spectral weight transfer from a coherent component at the Fermi level to an incoherent one at 1--2 eV below it. This behavior is similar to that of electron-doped ${\mathrm{SrTiO}}_{3}$. On the other hand, Nb $3d$ and $4p$ core level spectra exhibit a screening effect with an energy scale of 1--2 eV by the coherent Nb $4d$ electrons similar to $4d$ electron systems near Mott transitions. The energy scale indicates that electron correlation is involved in the metal to insulator transition in the present system, although the Nb $4d$ band is about 1/10 filled. The present results suggest a mechanism of electron localization due to atomic disorder and electron correlation.

International audience; We present the status of the art of the Archimedes experiment, devoted to measuring the debated interaction of quantum vacuum fluctuations and gravity. The method is essentially the weighing of the transition energy of a layered superconductor where the contribution of vacuum energy to the transition energy is expected to be relevant. The transition is obtained by modulating the temperature of the superconducting sample at a frequency of about 10 mHz and the expected change of weight is measured with a suitably designed high sensitivity cryogenic beam balance. In this paper, we present an overview of the experiment, discussing the expected signal to be measured, and presenting in particular the result of a prototype balance operated in our present laboratory. In the frequency range of the measurement, the sensitivity is affected mainly by seismic, thermal, sensor, and control noise. We discuss these points showing in particular the design of the cryogenic apparatus, the final balance, and the quiet seismic site that will host the final measurement.

We have studied temperature-driven effects on photoemission spectra of hollandite-type ${\mathrm{Ba}}_{x}{\mathrm{Ti}}_{8}{\mathrm{O}}_{16+\ensuremath{\delta}}$ across its metal-insulator transition (MIT) at 220 K by using surface-sensitive photon energies from 27 to 70 eV. The surface Ti $3d$ spectral weight was suppressed and shifted towards higher binding energy from the bulk if the surface was obtained by cleavage above the MIT temperature. The Ti $3d$ spectral weight was recovered once the sample was cooled across the MIT, indicating a transfer of Ti $3d$ electrons from the bulk to the surface across the MIT. The recovered Ti $3d$ spectral shape is consistent with the bulk-sensitive result and indicates strong localization character of the Ti $3d$ electron even in the metallic phase. Resonant photoemission spectroscopy with absorption from the Ti $3p$ core level exhibits resonances of the O $2p$-Ti $3d$ and O $2p$-Ti $4s,p$ hybridized states. The result suggests that the O $2p$-Ti $4s,p$ hybridization plays a role in the interplay between the bulk and the surface in ${\mathrm{Ba}}_{x}{\mathrm{Ti}}_{8}{\mathrm{O}}_{16+\ensuremath{\delta}}$.

Recently CeOBiS2 system without any fluorine doping is found to show superconductivity posing question on its origin. Using space resolved ARPES we have found a metallic phase embedded in the morphological defects and at the sample edges of stoichiometric CeOBiS2. While bulk of the sample is semiconducting, the embedded metallic phase is characterized by the usual electron pocket at X point, similar to the Fermi surface of doped BiS2-based superconductors. Typical size of the observed metallic domain is larger than the superconducting correlation length of the system suggesting that the observed superconductivity in undoped CeOBiS2 might be due to this embedded metallic phase at the defects. The results also suggest a possible way to develop new systems by manipulation of the defects in these chalcogenides with structural instability.

The local structure of La(Fe1−x Mn x )AsO has been investigated using temperature dependent Fe K-edge extended x-ray absorption fine structure (EXAFS) measurements. The EXAFS data reveal distinct behavior of Fe–As and Fe–Fe atomic displacements with a clear boundary between x ⩽ 0.02 and x > 0.02. The Fe–As bondlength shows a gradual thermal expansion while the Fe–Fe bond manifests a temperature dependent anomaly at ∼180 K for x > 0.02. It is interesting to find characteristically different nature of Fe–As and Fe–Fe bondlengths shown by the temperature dependent mean square relative displacements. Indeed, the Fe–As bond, stiffer than that of the Fe–Fe, gets softer for x ⩽ 0.02 and hardly shows any change for x > 0.02. On the other hand, Fe–Fe bond tends to be stiffer for x ⩽ 0.02 followed by a substantial softening for x > 0.02. Such a distinction has been seen also in the As K-edge x-ray absorption near edge structure, probing local geometry around As atom together with the valence electronic structure. The results suggest that local atomic displacements by Mn substitution inducing increased iron local magnetic moment that should be the main reason for its dramatic effect in iron-based superconductors.

We have investigated the local structure of layered La 1 − x Ce x OBiSSe system by Bi L 3 -edge extended X-ray absorption fine structure (EXAFS) measurements for different Ce substitutions. Ce L 3 -edge X-ray absorption spectroscopy (XAS) has been used to evaluate the Ce valence responsible for the self-doping in this system. We have found that the local distortion, determined by the separation between two Bi-Ch distances within the BiCh 2 -layer (Ch=S,Se), is quickly suppressed by Ce substitution while the axial Bi-S2 bond elongates. Ce L 3 -edge XAS reveals a coexistence of Ce 3 + and Ce 4 + in which the Ce 4 + weight decreases, an indication of a partial breaking of R E -S-Bi ( R E =La/Ce) charge transfer channel with Ce substitution. The results suggest that interaction between R E O spacer layer and BiCh 2 layer, dictated by the out-of-plane Bi-S2 distance, has a significant role in triggering superconductivity in the title system, with the in-plane distortion controlling the charge mobility within the BiCh 2 -layer.

We have studied the valence electronic structure of Ag1-xSn1+xSe2 (x = 0.0, 0.1, 0.2, 0.25) and SnSe (x = 1.0) by a combined analysis of X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS) measurements. Both XAS and XPS reveal an increase in electron carriers in the system with x (i.e. excess Sn concentration) for 0 ≤ x ≤ 0.25. The core-level spectra (Sn 3d, Ag 3d and Se 3d) show that the charge state of Ag is almost 1+, while that of of Sn splits into Sn2+ and Sn4+ (providing clear evidence of valence skipping for the first time) with a concomitant splitting of Se into Se2- and Se2-δ states. The x dependence of the split components in Sn and Se together with the Se-K edge XAS reveals that the Se valence state may have an essential role in the transport properties of this system.

We have studied electronic properties of ${\mathrm{BaV}}_{10}{\mathrm{O}}_{15}$ in the intermediate-temperature phase as well as in the high-temperature metallic phase by using hard x-ray photoemission spectroscopy (HAXPES). The V $2p$ HAXPES show a shift in the high-temperature phase between 300 and 245 K which is similar to the shift of spectral weight near the Fermi edge. The binding energy of the O $1\mathit{s}$ HAXPES peak does not change except a slight shift of the lower binding energy edge in the opposite direction between 300 and 180 K across the transition to the intermediate-temperature phase. This behavior is in sharp contrast to the transition to the low-temperature insulating phase where V $2p$ and O $1s$ HAXPES show dramatic shifts in the same direction. This indicates that the charge-orbital change in the intermediate-temperature phase is driven by the correlated V $3d$ electrons and is electronic. The ${\mathrm{V}}^{2.5+}\text{\ensuremath{-}}{\mathrm{V}}^{2.5+}$ bond ordering is related to the metallic contribution and gradually decreases with cooling from 300 K. The valence-band HAXPES show the metallic features of the pseudogap behavior near the Fermi edge in and above the intermediate-temperature phase due to ${\mathrm{V}}^{2.5+}\text{\ensuremath{-}}{\mathrm{V}}^{3+}$ charge fluctuation. The magnitude of the pseudogap increases from 300 to 180 K in parallel with the gradual breaking of the ${\mathrm{V}}^{2.5+}\text{\ensuremath{-}}{\mathrm{V}}^{2.5+}$ bond and formation of trimers.

We have studied the electronic structure of the stripe-type charge-orbital ordered phase of IrTe2 by means of angle-resolved photoemission spectroscopy. An electron pocket at the Brillouin zone boundary and hole Fermi surfaces around its center are clearly observed in agreement with the band structure calculation for the stripe-type charge-orbital ordered phase. The present study indicates that the hole and electron Fermi surfaces can survive due to the strong Te 5p spin-orbit coupling even under the charge-orbital order. The participant of the Te 5p orbitals to the conduction band provides an interesting interplay between the charge-orbital order and the spin-orbit interaction in IrTe2.

Spectroscopic techniques, including photoelectron spectroscopy, diffuse reflectance, and x-ray absorption, are used to investigate the electronic structure and the local structure of LaOBiS$_{2-x}$Se$_x$ thermoelectric material. It is found that Se substitution effectively suppresses local distortion, that can be responsible for the increased carrier mobility together with a change in the electronic structure. The results suggest a possible way to control thermoelectric properties by tuning of the local crystal structure of these materials., Comment: 6 pages, 4 figures, 1 table, J. Appl. Phys. (in press)

Stoichiometric ${\mathrm{EuFBiS}}_{2}$ with mixed valent Eu shows self-doped superconductivity at low temperatures due to the Eu-to-Bi charge transfer. The metallic/nonmetallic bistability of the ${\mathrm{BiS}}_{2}$ layer can couple with the valence fluctuation of Eu and provide a highly susceptible electronic state. Here, we report space-resolved photoemission measurements on ${\mathrm{EuFBiS}}_{2}$ revealing an inhomogeneous charge distribution with the coexistence of metallic and nonmetallic phases at mesoscopic length scales. Angle-resolved photoemission measurements using a submicron beam size have confirmed a clear Fermi surface around the zone boundaries in the metallic region, typically observed in a doped system, while it can be hardly seen in the nonmetallic region. Density functional theory calculations suggest that the out-of-plane S atom position in the structure is one of the important factors for the self-doping in this material.

NaSn(2)As(2 )is mechanically exfoliable layered van der Waals (vdW) Zintl phase that is getting interesting due to its low thermal conductivity and recently observed superconductivity. Here, we have investigated the temperature dependent local structure of NaSn2As2 by a combined analysis of As K-edge and Sn K-edge extended x-ray absorption fine structure measurements. The system is intrinsically disordered with the interatomic distances largely consistent to those estimated by average structure measurements. The stretching force constants of different bond distances have been determined using temperature dependent mean square relative displacements. The Sn-As distance is the strongest bond in this system, having covalent nature, unlike the weaker interlayer distances which are characterized by vdW type bonding. Among them, As-Na distance is slightly weaker than Sn-Sn(i) below similar to 200 K and tends to get stronger above this temperature. The anomalous behavior of As-Na bond suggests that the mechanical exfoliation in this system is likely to be temperature dependent. The anomaly in the interlayer atomic correlations may be due to a charge density wave-like instability around this temperature, indicated by earlier experiments. The local structure and disorder are discussed in relation to the physical properties of NaSn2As2.

The high pressure tolerance of cysts of Artemia salina was investigated up to several GPa in water. No survival was observed after exposure to 1.0GPa for 15min. After exposure to 2.0GPa for the same time duration, the hatching rate had recovered to 33%, but decreased to 8% following compression at 7.5GPa. This contrasts with results using Fluorinert as the pressure-transmitting medium where 80-88% recovery was observed. The lower survival rate in water is accompanied by swelling of the eggs, indicating that liquid H2O close to the ice-VI crystallization pressure penetrated inside the eggs. This pressure exceeds the stability limit for proteins and other key biomolecules components within the embryos that could not be resuscitated. Rehydration takes several minutes and so was not completed for all samples compressed to higher pressures, prior to ice-VI formation, resulting in renewed survival. However H2O penetration inside the shell resulted in increased mortality.

We report the experimental results of temperature dependent polarized As K-edge extended x-ray absorption fine structure (EXAFS) of LaFe1-xCoxAsO (x=0.0 and 0.11) single-crystals. By aligning the Fe-As bond direction in the direction of the x-ray beam polarization we have been able to identify an anomaly in the Fe-As bond correlations at the tetragonal to orthorhombic transition at 150K, while previous investigations with standard unpolarized EXAFS of undoped LaFeAsO powder samples were not able to detect any such anomaly. Using our approach we have been able to identify in the superconducting doped sample, LaFe0.89Co0.11AsO, a broad anomaly around 60 K. The low temperature anomaly has good correlations with the temperature dependence of several properties like resistivity, magnetic susceptibility, linear thermal expansion, etc indicating the emergence of the dynamical oscillations of the Fe - As pairs, 7 pages, 3 figures

The effect of electronic correlation on $\mathrm{WT}{\mathrm{e}}_{2}$ has been investigated by means of angle-resolved photoemission spectroscopy (ARPES) and band-structure calculation. In the ARPES results, the valence band top with Te $5p$ character reaches the Fermi level and forms complicated hole pockets around the zone center. In addition, two electron pockets are observed besides the hole pockets. The position of the electron pockets is inconsistent with the prediction of band calculation, suggesting the importance of electronic correlation in $\mathrm{WT}{\mathrm{e}}_{2}$. The present analysis indicates the correlation effect is associated with the excitonic coupling between the W $5d$ electron and Te $5p$ hole bands.

We have investigated the electronic properties of ${\mathrm{BiS}}_{2}$-based superconductors by using x-ray photoemission spectroscopy (XPS). In going from $x=0.3$ to 0.5 in ${\mathrm{PrO}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}{\mathrm{BiS}}_{2}$, the Pr $3d$ and Pr $4d$ peaks are shifted by $\ensuremath{\sim}0.10\ifmmode\pm\else\textpm\fi{}0.05$ eV from the Fermi level, partially consistent with the electron doping. In ${\mathrm{PrO}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}{\mathrm{BiS}}_{2}$, the ${\mathrm{Pr}}^{3+}\ensuremath{-}{\mathrm{Pr}}^{4+}$ mixed valence remains unchanged with the electron doping from $x=0.3$ to 0.5. In ${\mathrm{CeO}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}{\mathrm{BiS}}_{2}$, the doped electrons for $x=0.5$ almost suppress the ${\mathrm{Ce}}^{3+}\ensuremath{-}{\mathrm{Ce}}^{4+}$ valence fluctuation. Although the core-level peaks are also shifted by $\ensuremath{\sim}0.10\ifmmode\pm\else\textpm\fi{}0.05$ eV towards the higher-binding-energy side with the electron doping from $x=0$ to 0.5 in ${\mathrm{CeO}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}{\mathrm{BiS}}_{2}$, the Bi $4{f}_{7/2}$ binding-energy shift is higher in the Pr system compared with the Ce system. The present results suggest that the doped electrons increase orbital occupations in the rare-earth $4f$ orbitals at the valence band and show valence fluctuations differently in the two systems.

The local structures of 122-type paradium arsenides, namely BaPd2As2 and SrPd2As2, are examined by As K-edge extended x-ray absorption fine structure measurements to find a possible correlation between the variation of their superconducting transition temperature and the local structure. The local atomic distances are found to be consistent with average distances measured by diffraction techniques. The temperature dependence of mean square relative displacements reveal that, while BaPd2As2 is characterized by a local As-Pd soft mode, albeit with larger atomic disorder, SrPd2As2 shows anomalous As-Pd correlations with a kink at similar to 160 K due to hardening by raising temperature. We have discussed implications of these results and possible mechanisms of differing superconducting transition temperature in relation with the structural instability.

We report an angle-resolved photoemission spectroscopy study on NaSn2As2 in which a Sn 5p band is expected to provide interesting Fermi surface geometry with hole-like and electron-like curvatures....

We have investigated the local structure of differently charged NaxCoO2 cathode material as a function of temperature by Co K-edge X-ray absorption fine structure (EXAFS) measurements. We have found that the charge/discharge process has a direct effect on the bond characteristics of the cathode in the Na-ion batteries. The results reveal that the local Co–O bonds get softer, while the Co–Co bonds hardly show any change during discharge (sodiation). The present study underlines the key role of local atomic displacements in diffusion and the reversibility of ions in cathodes for batteries and points toward the feasibility of NaxCoO2 to be used as a cathode material. The results are discussed in comparison with the lithiation/delithiation of LixCoO2 battery materials.

Ab initio X-ray absorption near edge structure (XANES) calculations for FeSe x Te 1− x , using a structural model that combines FeSe and FeTe phases at the nanoscale, are compared with Fe K -edge XANES measurements in the “pre-edge” region. The important aspects of this model are (i) magnetic order in the FeTe phase; (ii) Se and Te atoms placed randomly in both FeSe and FeTe crystallographic positions and; (iii) the two distinct distances for Fe–Se and Fe–Te of the bulk phases. The calculated spectra reproduce the observed increase of spectral weight in the experiments on FeSe x Te 1− x with Se concentration. This is consistent with an inhomogeneous local electronic structure of FeSe x Te 1− x . Additionally, we have calculated projected electronic density of d -states for the Fe atom, revealing increased spectral weight in the “pre-edge” region of the XANES spectra, which correlates with the increase in Se concentration. The decrease of calculated Fe d -density of states for the Fermi level, N ( e F ), for high Te content is consistent with the suppression of superconductivity in the title system.

${\mathrm{Ta}}_{2}{\mathrm{NiS}}_{5}$ is supposed to be a simple semiconductor in which excitonic instability of ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ is suppressed due to its large band gap. However, the Ni $2p$ core-level photoemission of ${\mathrm{Ta}}_{2}{\mathrm{NiS}}_{5}$ exhibits a satellite indicating Ni $3d$ orbitals are mixed into its conduction band as expected in an excitonic insulator. The valence band does not show dispersion flattening and spectral sharpening which are fingerprints of an excitonic insulator. Instead, Ni $3p\ensuremath{-}3d$ resonant photoemission indicates Mottness of the Ni $3d$ electron in ${\mathrm{Ta}}_{2}{\mathrm{NiS}}_{5}$ with negative charge-transfer energy. The present results show that ${\mathrm{Ta}}_{2}{\mathrm{NiS}}_{5}$ can be viewed as a valence bond insulator with a band gap exceeding the exciton binding energy.

We have studied a charge-orbital driven metal-insulator transition (MIT) in hollandite-type ${\mathrm{Ba}}_{x}{\mathrm{Ti}}_{8}{\mathrm{O}}_{16+\ensuremath{\delta}}$ by means of hard x-ray photoemission spectroscopy (HAXPES). The Ti $2p$ HAXPES indicates strong ${\mathrm{Ti}}^{3+}$/${\mathrm{Ti}}^{4+}$ charge fluctuation in the metallic phase above the MIT temperature. The metallic phase is characterized by a power-law spectral function near the Fermi level which would be a signature of bad metal with non-Drude polaronic behavior. The power-law spectral shape is associated with the large Seebeck coefficient of the metallic phase in ${\mathrm{Ba}}_{x}{\mathrm{Ti}}_{8}{\mathrm{O}}_{16+\ensuremath{\delta}}$.

The local structure of correlated spin-orbit insulator Sr$_{2-x}$M$_x$IrO$_4$ (M = K, La) has been investigated by Ir L$_3$-edge extended x-ray absorption fine structure measurements. The measurements were performed as a function of temperature for different dopings induced by substitution of Sr with La or K. It is found that Ir-O bonds have strong covalency and they hardly show any change across the N\'eel temperature. In the studied doping range, neither Ir-O bonds nor their dynamics, measured by their mean square relative displacements, show any appreciable change upon carrier doping, indicating possibility of a nanoscale phase separation in the doped system. On the other hand, there is a large increase of the static disorder in Ir-Sr correlation, larger for K doping than La doping. Similarities and differences with respect to the local lattice displacements in cuprates are briefly discussed., Comment: Main text: 6 pages, 4 figures, Supplemental information: 2 pages, 2 figures

We have studied the electronic structure of SnSe and Na-doped SnSe by means of angle-resolved photoemission spectroscopy. The valence-band top reaches the Fermi level by the Na doping, indicating that Na-doped SnSe can be viewed as a degenerate semiconductor. However, in the Na-doped system, the chemical potential shift with temperature is unexpectedly large and is apparently inconsistent with the degenerate semiconductor picture. The large chemical potential shift and anomalous spectral shape are key ingredients for an understanding of the novel metallic state with the large thermoelectric performance in Na-doped SnSe.

We have studied the valence electronic structure of Ag

We have performed scanning photoemission spectromicroscopy of ${\mathrm{BaV}}_{10}{\mathrm{O}}_{15}$ across the metal-insulator transition at 123 K, which is accompanied by V $3d$ charge/orbital order and V trimerization. Nucleation of metallic domains is observed at the cleaved surface of ${\mathrm{BaV}}_{10}{\mathrm{O}}_{15}$ single crystals, similar to Cr-doped ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ in which electronic configurations of ${\mathrm{Cr}}^{3+}$ and ${\mathrm{V}}^{3+}$ are the same as those of ${\mathrm{V}}^{2+}$ and ${\mathrm{V}}^{3+}$ in ${\mathrm{BaV}}_{10}{\mathrm{O}}_{15}$. Typical domain size is $\ensuremath{\sim}5\text{--}10\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$ at 150 K, just above the transition temperature. The metallic domains continuously grow up to 240 K, well above the transition temperature. The temperature evolution of the metallic phase in ${\mathrm{BaV}}_{10}{\mathrm{O}}_{15}$ is different from that of Cr-doped ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$, probably due to the charge degrees of freedom in ${\mathrm{BaV}}_{10}{\mathrm{O}}_{15}$.

We report an angle-resolved photoemission spectroscopy (ARPES) study of ${\mathrm{Li}}_{x}{\mathrm{CoO}}_{2}$ single crystals which have a hole-doped ${\mathrm{CoO}}_{2}$ triangular lattice. Similar to ${\mathrm{Na}}_{x}{\mathrm{CoO}}_{2}$, the Co $3d\phantom{\rule{4pt}{0ex}}{a}_{1g}$ band crosses the Fermi level with strongly renormalized band dispersion while the Co $3d\phantom{\rule{4pt}{0ex}}{e}_{g}^{\ensuremath{'}}$ bands are fully occupied in ${\mathrm{Li}}_{x}{\mathrm{CoO}}_{2}$ ($x=0.46$ and 0.71). At $x=0.46$, the Fermi surface area is consistent with the bulk hole concentration indicating that the ARPES result represents the bulk electronic structure. On the other hand, at $x=0.71$, the Fermi surface area is larger than the expectation which can be associated with the inhomogeneous distribution of Li reported in the previous scanning tunneling microscopy study by Iwaya et al. [Phys. Rev. Lett. 111, 126104 (2013)]. However, the Co $3d$ peak is systematically shifted towards the Fermi level with hole doping excluding phase separation between hole rich and hole poor regions in the bulk. Therefore, the deviation of the Fermi surface area at $x=0.71$ can be attributed to hole redistribution at the surface avoiding polar catastrophe. The bulk Fermi surface of Co $3d\phantom{\rule{4pt}{0ex}}{a}_{1g}$ is very robust around $x=0.5$ even in the topmost ${\mathrm{CoO}}_{2}$ layer due to the absence of the polar catastrophe.

The electronic structure of the lightly electron-doped correlated spin-orbit insulator Sr2IrO4 has been studied by angle-resolved photoelectron spectroscopy. We have observed the coexistence of a lower Hubbard band and an in-gap band; the momentum dependence of the latter traces that of the band calculations without on-site Coulomb repulsion. The in-gap state remained anisotropically gapped in all observed momentum areas, forming a remnant Fermi-surface state, evolving towards the Fermi energy by carrier doping. These experimental results show a striking similarity with those observed in deeply underdoped cuprates, suggesting the common nature of the nodal liquid states observed in both compounds.

We have studied the nanoscale structure and unoccupied electronic states in FeSe1-xTex by a combined analysis of Se K, Te L1 and Fe K-edges X-ray absorption measurements. Extended X-ray absorption fine structure (EXAFS) results show that iron-chalcogen (Fe-Se and Fe-Te) distances in ternary FeSe1-xTex are similar to those measured for binary FeSe and FeTe. The local Fe-Se/Te distances determined by different absorption edges fit well in the characteristic Z-plot of random alloys, providing unambiguous support to the inhomogeneous nanoscale structure of the ternary FeSe1-xTex system. X-ray absorption near-edge structure (XANES) spectra reveal a gradual evolution of the unoccupied valence electronic states as a function of Te-substitution in FeSe1-xTex. The Fe 3d-Se 4p/Te 5p hybridization is found to decrease with Te-substitution, accompanied by an increase in unoccupied Se 4p states and a decrease in unoccupied Te 5p states. The results are discussed in the frame of local inhomogeneity in the FeSe1-xTex system driven by random alloying of Se/Te atoms.