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Proceedings of the National Academy of Sciences of the United States of America 117(48), 30220 - 30227 (2020). doi:10.1073/pnas.2005701117, Using inelastic X-ray scattering beyond the dipole limit and hard X-ray photoelectron spectroscopy we establish the dual nature of the U 5f electrons in UM$_2$Si$_2$ (M = Pd, Ni, Ru, Fe), regardless of their degree of delocalization. We have observed that the compounds have in common a local atomic-like state that is well described by the U 5f$^2$ configuration with the $Γ^{(1)}_1$ and $Γ_2$ quasi-doublet symmetry. The amount of the U 5f$^3$ configuration, however, varies considerably across the UM$_2$Si$_2$ series, indicating an increase of U 5f itineracy in going from M = Pd to Ni to Ru and to the Fe compound. The identified electronic states explain the formation of the very large ordered magnetic moments in UPd$_2$Si$_2$ and UNi$_2$Si$_2$, the availability of orbital degrees of freedom needed for the hidden order in URu2Si2 to occur, as well as the appearance of Pauli paramagnetism in UFe$_2$Si$_2$. A unified and systematic picture of the UM$_2$Si$_2$ compounds may now be drawn, thereby providing suggestions for additional experiments to induce hidden order and/or superconductivity in U compounds with the tetragonal body-centered ThCr$_2$Si$_2$ structure., Published by National Acad. of Sciences, Washington, DC

Physical review / X 11(1), 011002 (2021). doi:10.1103/PhysRevX.11.011002, Herein we show that nonresonant inelastic x-ray scattering involving an $s$ core level is a powerful spectroscopic method to characterize the excited states of transition metal compounds. The spherical charge distribution of the $s$ core hole allows the orientational dependence of the intensities of the various spectral features to produce a spatial charge image of the associated multiplet states in a straightforward manner, thereby facilitating the identification of their orbital character. In addition, the $s$ core hole does not add an extra orbital angular momentum component to the multiplet structure so that the well-established Sugano-Tanabe-Kamimura diagrams can be used for the analysis of the spectra. For $\alpha$-MnS we observe the spherical charge density corresponding to its high-spin $3d^5$ ($^6A_1$) ground state configuration and we were able to selectively image its excited states and identify them as $t_{2g}$ ($^5T_2$) and $e_g$ ($^5E$) with an energy splitting $10Dq$ of 0.78 eV., Published by APS, College Park, Md.

The crystal-field ground state wave function of CeCu$_2$Si$_2$ has been investigated with linear polarized $M$-edge x-ray absorption spectroscopy from 250mK to 250K, thus covering the superconducting ($T_{\text{c}}$=0.6K), the Kondo ($T_{\text{K}}$$\approx$20K) as well as the Curie-Weiss regime. The comparison with full-multiplet calculations shows that the temperature dependence of the experimental linear dichroism is well explained with a $\Gamma_7^{(1)}$ crystal-field ground-state and the thermal population of excited states at around 30meV. The crystal-field scheme does not change throughout the entire temperature range thus making the scenario of orbital switching unlikely. Spectroscopic evidence for the presence of the Ce 4$f^0$ configuration in the ground state is consistent with the possibility for a multi-orbital character of the ground state. We estimate from the Kondo temperature and crystal-field splitting energies that several percents of the higher lying $\Gamma_6$ state and $\Gamma_7^{(2)}$ crystal-field states are mixed into the primarily $\Gamma_7^{(1)}$ ground state. This estimate is also supported by re-normalized band-structure calculations that uses the experimentally determined crystal-field scheme., Comment: 8 pages, 5 figures

The 4$f$ orbital shape correlates with the ground state of the strongly correlated Ce$M$In${}_{5}$ family, with $M$=Co, Rh, and Ir. The remaining question as to how these orbitals are oriented has now been answered through nonresonant inelastic x-ray scattering (NIXS) measurements. Quantitative analysis reveals a hybridization-induced contribution of the first excited crystal-field state to the ground state of superconducting CeCoIn${}_{5}$, an important finding that suggests a degeneracy larger than two and that constrains realistic calculations of the electronic structure.

Nature Communications 10(1), 5447 (2019). doi:10.1038/s41467-019-13273-4, The one-dimensional cobaltate Ca$_3$Co$_2$O$_6$ is an intriguing material having an unconventional magnetic structure, displaying quantum tunneling phenomena in its magnetization. Using a newly developed experimental method, $s$-core-level non-resonant inelastic x-ray scattering ($s$-NIXS), we were able to image the atomic Co 3$d$ orbital that is responsible for the Ising magnetism in this system. We can directly observe that corrections to the commonly accepted ideal prismatic trigonal crystal field scheme occur in Ca$_3$Co$_2$O$_6$, and it is the complex $d_2$ orbital occupied by the sixth electron at the high-spin Co$^{3+}_\text{trig}$ ($d^6$) sites that generates the Ising-like behavior. The ability to directly relate the orbital occupation with the local crystal structure is essential to model the magnetic properties of this system., Published by Nature Publishing Group UK, [London]

Nonresonant inelastic x-ray scattering (NIXS) has been performed on single crystals of ${\mathrm{UO}}_{2}$ to study the directional dependence of higher-order-multipole scattering from the uranium ${O}_{4,5}$ edges (90--110 eV). By comparing the experimental results with theoretical calculations the symmetry of the ground state is confirmed directly as the crystal-field (CF) ${\mathrm{\ensuremath{\Gamma}}}_{5}$ triplet state within the $J=4$ manifold. The results demonstrate that the directional dichroism of the NIXS spectra is sensitive to the CF strength and establish NIXS as a tool for probing CF interactions quantitatively.

We have investigated the local low-energy excitations in CeRu4Sn6, a material discussed recently in the framework of strongly correlated Weyl semimetals, by means of Ce M-5 resonant inelastic x-ray scattering (RIXS). The availability of both F-2(5/2) and F-2(7/2) excitations of the Ce 4f(1) configuration in the spectra allows for the determination of the crystal-electric field (CEF) parameters that explain quantitatively the high-temperature anisotropy of the magnetic susceptibility. The absence of an azimuthal dependence in the spectra indicates that all CEF states are close to being rotational symmetric. We show further that the non-negligible impact of the (sic)(6)(0) parameter on the ground state of CeRu4Sn6 leads to a reduction of the magnetic moment mu(c) due to multiplet intermixing. This improves the agreement between CEF calculations and the experimentally determined magnetic susceptibility considerably at low temperatures. Deviations that persist at low temperatures for fields within the tetragonal plane are attributed to the Kondo interaction between 4f and conduction electrons. The RIXS results are consistent with inelastic neutron scattering data and are compared to the predictions from ab initio based electronic structure calculations.

Yb$_2$Si$_2$Al may be a prototype for exploring different aspects of the Shastry-Sutherland lattice, formed by planes of orthogonally coupled Yb ions. Measurements of the magnetic susceptibility find incoherently fluctuating Yb$^{3+}$ moments coexisting with a weakly correlated metallic state that is confirmed by measurements of the electrical resistivity. Increasing signs of Kondo coherence are found with decreasing temperature, including an enhanced Sommerfeld coefficient and Kadowaki-Woods ratio that signal that the metallic state found at the lowest temperatures is a Fermi liquid where correlations have become significantly stronger. A pronounced peak in the electronic and magnetic specific heat indicates that the coupling of the Yb moments to the conduction electrons leads to an effective Kondo temperature that is approximately 30 K. The valence of Yb$_2$Si$_2$Al has been investigated with electron spectroscopy methods. Yb$_2$Si$_2$Al is found to be strongly intermediate valent ($v_F=2.68(2)$ at 80 K). Taken together, these experimental data are consistent with a scenario where a coherent Kondo lattice forms in Yb$_2$Si$_2$Al from an incoherently fluctuating ensemble of Yb moments with incomplete Kondo compensation, and strong intermediate valence character., Submitted to Physical Review B

We investigated the crystal-electric field ground state of the $4f$ manifold in the strongly correlated topological insulator ${\mathrm{SmB}}_{6}$ using core-level nonresonant inelastic x-ray scattering. The directional dependence of the scattering function that arises from higher multipole transitions establishes unambiguously that the ${\mathrm{\ensuremath{\Gamma}}}_{8}$ quartet state of the Sm ${f}^{5}\text{ }\text{ }J=5/2$ configuration governs the ground-state symmetry and, hence, the topological properties of ${\mathrm{SmB}}_{6}$. Our findings contradict the results of density functional calculations reported so far.

We present linear polarization-dependent soft x-ray absorption spectroscopy data at the Ce $M_{4,5}$ edges of Cd and Sn doped CeCoIn$_5$. The 4$f$ ground state wave functions have been determined for their superconducting, antiferromagnetic and paramagnetic ground states. The absence of changes in the wave functions in CeCo(In$_{1-x}$Cd$_x$)$_5$ suggests the 4$f$\,--\,conduction electron ($cf$) hybridization is not affected by globally Cd doping, thus supporting the interpretation of magnetic droplets nucleating long range magnetic order. This is contrasted by changes in the wave function due to Sn substitution. Increasing Sn in CeCo(In$_{1-y}$Sn$_y$)$_5$ compresses the 4$f$ orbitals into the tetragonal plane of these materials, suggesting enhanced $cf$ hybridization with the in-plane In(1) atoms and a homogeneous altering of the electronic structure. As these experiments show, the 4$f$ wave functions are a very sensitive probe of small changes in the hybridization of 4$f$ and conduction electrons, even conveying information about direction dependencies., 6 pages, 4 figures

epl 117(1), 17003 (2017). doi:10.1209/0295-5075/117/17003, We investigated the ground-state symmetry of the cubic hidden order compound CeB$_6$ by means of core level non-resonant inelastic x-ray scattering (NIXS). The information is obtained from the directional dependence of the scattering function that arises from higher than dipole transitions. Our new method confirms that the ground state is well described using a localized crystal-field model assuming a Γ$_8$ quartet ground state., Published by IOP Publ., Les-Ulis

The crystal-field ground-state wave functions of the tetragonal, magnetically ordering Kondo lattice materials $\mathrm{Ce}M{\mathrm{Al}}_{4}{\mathrm{Si}}_{2}$ $(M=\text{Rh}$, Ir, and Pt) are determined with low-temperature linearly polarized soft-x-ray absorption spectroscopy, and estimates for the crystal-field splittings are given from the temperature evolution of the linear dichroism. Values for the dominant exchange field in the magnetically ordered phases can be obtained from fitting the influence of magnetic order on the linear dichroism. The direction of the required exchange field is $\ensuremath{\parallel}\phantom{\rule{0.16em}{0ex}}c$ for the antiferromagnetic Rh and Ir compounds, with the corresponding strength of the order of ${\ensuremath{\lambda}}_{\text{ex}}\ensuremath{\approx}6\phantom{\rule{4pt}{0ex}}\text{meV}$ (65 K). Furthermore, the presence of Kondo screening in the Rh and Ir compound is demonstrated on the basis of the absorption due to ${f}^{0}$ in the initial state.

The second-order phase transition into a hidden order phase in URu$_2$Si$_2$ goes along with an order parameter which is still a mystery, despite 30 years of research. However, it is understood that the symmetry of the order parameter must be related to the symmetry of the low lying local electronic $f$-states. Here we present results of a novel spectroscopy, namely core-level non-resonant inelastic x-ray scattering (NIXS). This method allows for the measurement of local high-multipole excitations and it is bulk sensitive. The observed anisotropy of the scattering function unambiguously shows that the 5$f$ ground state wave function is composed mainly, but essentially not purely, of the $\Gamma_1$ with majority $J_z$ =$|4\rangle$ + $|-4\rangle$ and/or $\Gamma_2$ singlet states., Comment: 9 pages, 6 figures

Significance The ground state of materials with strong electronic correlations depends on a delicate balance among competing interactions. The strongly correlated compounds Ce M In 5 , with M = Co, Rh, and Ir, exhibit superconducting and magnetic ground states as well as Fermi surface changes upon substituting one M element for another and become even higher temperature superconductors when Ce is substituted by Pu. They are therefore recognized as important model systems in which a search for parameters correlating with the occurrence of these ground states could be successful. The present X-ray absorption study of CeRh 1− x Ir x In 5 reveals that anisotropy of the Ce 4 f -wave function is a significant parameter that is highly sensitive to the ground-state formation and should be taken into account when modeling these systems.

Topological insulators form a novel state of matter that provides new opportunities to create unique quantum phenomena. While the materials used so far are based on semiconductors, recent theoretical studies predict that also strongly correlated systems can show non-trivial topological properties, thereby allowing even the emergence of surface phenomena that are not possible with topological band insulators. From a practical point of view, it is also expected that strong correlations will reduce the disturbing impact of defects or impurities, and at the same increase the Fermi velocities of the topological surface states. The challenge is now to discover such correlated materials. Here, using advanced x-ray spectroscopies in combination with band structure calculations, we infer that CeRu$_4$Sn$_6$ is a strongly correlated material with non-trivial topology., Comment: 10 pages, 6 figures, submitted to Scientific Reports

Here we present linear-polarization-dependent soft x-ray absorption spectroscopy data at the Ce ${M}_{4,5}$ edges of CeOs${}_{2}$Al${}_{10}$ and CeFe${}_{2}$Al${}_{10}$. Despite the strong hybridization between $4f$ and conduction electrons and the existence of spin gaps as seen in inelastic neutron scattering, we were able to determine the crystal field ground state wave functions by combining our spectroscopy data with magnetization measurements. The results quantitatively explain the small ordered moment along $c$ and the measured magnetic moment along the easy $a$ axis in CeOs${}_{2}$Al${}_{10}$.

We report a comparative neutron inelastic-scattering study of single-crystal and polycrystalline samples of ${\mathrm{CePd}}_{3}$ with the aim to resolve conflicting claims concerning the form of the paramagnetic spectral response of the compound. The present measurements show that the inelastic scattering particularly at low scattering angles is very similar for both samples. We find also that the observed scattering at energies below 30 meV is mostly nonmagnetic. At low angles it is dominated by multiple-scattering processes in the relatively large samples used for the measurements. Magnetic scattering occurs predominantly at high energies and can be represented by a single-ion spectral function centered on a characteristic energy of \ensuremath{\sim}50\char21{}55 meV, in good accord with previous findings from time-of-flight and polarized neutron measurements on a triple-axis spectrometer. \textcopyright{} 1996 The American Physical Society.

We have succeeded in establishing the crystal-field ground state of CeRu${}_{2}$Al${}_{10}$, an orthorhombic intermetallic compound recently identified as a Kondo insulator. Using polarization-dependent soft x-ray absorption spectroscopy at the Ce ${M}_{4,5}$ edges, together with input from inelastic neutron and magnetic susceptibility experiments, we were able to determine unambiguously the orbital occupation of the $4f$ shell and to explain quantitatively both the measured magnetic moment along the easy $a$ axis and the small ordered moment along the $c$ axis. The results provide not only a platform for a realistic modeling of the spin and charge gap of CeRu${}_{2}$Al${}_{10}$, but demonstrate also the potential for soft x-ray absorption spectroscopy to obtain information not easily accessible by neutron techniques for the study of Kondo insulators in general.

We have successfully determined the hitherto unknown sign of the ${B}_{4}^{4}$ Stevens crystal-field parameter of the tetragonal heavy-fermion compound ${\mathrm{CeCu}}_{2}{\mathrm{Si}}_{2}$ using vector $\stackrel{^}{\mathbf{q}}$-dependent nonresonant inelastic x-ray scattering experiments at the cerium ${N}_{4,5}$ edge. The observed difference between the two different directions, $\stackrel{^}{\mathbf{q}}\ensuremath{\parallel}[100]$ and $\stackrel{^}{\mathbf{q}}\ensuremath{\parallel}[110]$, is due to the anisotropy of the crystal-field ground state in the (001) plane and is observable only because of the utilization of higher than dipole transitions possible in nonresonant inelastic x-ray scattering. This approach allows us to go beyond the specific limitations of dc magnetic susceptibility, inelastic neutron scattering, and soft x-ray spectroscopy, and provides us with a reliable information about the orbital state of the $4f$ electrons relevant for the quantitative modeling of the quasiparticles and their interactions in heavy-fermion systems.

We have been able to induce a linear dichroic signal in the Yb M(5) x-ray absorption white line of cubic YbInNi(4) by the application of a magnetic field. The nonzero integrated intensity of the magnetic field induced dichroic spectrum indicates a net noncubic 4f orbital polarization. A quantitative analysis of the temperature and field strength dependence establishes that the crystal-field ground state is a Γ(8) quartet. The results demonstrate the potential of magnetic field induced linear dichroism as a new powerful approach for the investigation of the degeneracy and orbital degrees of freedom of cubic heavy-fermion and Kondo systems.

Several genome-wide studies demonstrated that alternative splicing (AS) significantly increases the transcriptome complexity in plants. However, the impact of AS on the functional diversity of proteins is difficult to assess using genome-wide approaches. The availability of detailed sequence annotations for specific genes and gene families allows for a more detailed assessment of the potential effect of AS on their function. One example is the plant MADS-domain transcription factor family, members of which interact to form protein complexes that function in transcription regulation. Here, we perform an in silico analysis of the potential impact of AS on the protein-protein interaction capabilities of MIKC-type MADS-domain proteins. We first confirmed the expression of transcript isoforms resulting from predicted AS events. Expressed transcript isoforms were considered functional if they were likely to be translated and if their corresponding AS events either had an effect on predicted dimerisation motifs or occurred in regions known to be involved in multimeric complex formation, or otherwise, if their effect was conserved in different species. Nine out of twelve MIKC MADS-box genes predicted to produce multiple protein isoforms harbored putative functional AS events according to those criteria. AS events with conserved effects were only found at the borders of or within the K-box domain. We illustrate how AS can contribute to the evolution of interaction networks through an example of selective inclusion of a recently evolved interaction motif in the MADS AFFECTING FLOWERING1-3 (MAF1-3) subclade. Furthermore, we demonstrate the potential effect of an AS event in SHORT VEGETATIVE PHASE (SVP), resulting in the deletion of a short sequence stretch including a predicted interaction motif, by overexpression of the fully spliced and the alternatively spliced SVP transcripts. For most of the AS events we were able to formulate hypotheses about the potential impact on the interaction capabilities of the encoded MIKC proteins.

Linear-polarized soft-x-ray absorption (XAS) and inelastic neutron scattering (INS) experiments have been performed on $\text{Ce}M{\text{In}}_{5}$ with $M=\text{Rh}$, Ir, and Co to determine the crystal-field scheme and characteristic Kondo temperatures ${T}^{\ensuremath{\ast}}$ for the hybridization between $4f$ and conduction electrons. The ground-state wave functions are determined from the polarization-dependent soft-XAS data at the cerium ${M}_{4,5}$ edge and the crystal-field splittings from INS. The characteristic temperature ${T}^{\ensuremath{\ast}}$ has been determined from the line widths of the neutron scattering data. We find that the quasielastic linewidths of the superconducting compounds ${\text{CeCoIn}}_{5}$ and ${\text{CeIrIn}}_{5}$ are comparable with the low-energy crystal-field splitting.

Neutron scattering has proved to be an effective probe of high-energy magnetic excitations. Recent measurements on AnO2 (An=U, Np, Pu) performed at spallation source-based spectrometers have made important contributions in the understanding of the crystal field potential in such systems. The experimental results are consistent with a fairly constant potential across the series and suggest that the ground state wave functions may be expressed almost entirely within a single J-manifold.

J. Phys. I France APRIL PAGE Classification Physics Abstracts 75.30M Magnetic ordering Bonville(~), B. Canaud(~), J. HamnJann(~), Jdhanno(~), A. Severing(~) and Z. Fisk(~) P. G. Service les Los Laue-Langevin, RAsumA temp6rature basse gn6tique (TN Yb~+ K), nous rapport par 4vidence en France au notable M6ssbauer l~°Yb sur propr16t6s des h antiferroma- YbAuCu4. Dans la phase de 20 $l du spontan6 h saturation moment lourds r4duction T7 de champ cristallin, et magn4tique entre les ions. Nous fondamental l'interaction de U-S-A- December1991) 61ectrons l'4tat de form Mexico New spectroscopie par une mesurons moment anisotropie une Grenoble, pr6sentons une 4tude du compos6 cubique k Nous D6partement de Recherche sur l'Etat Condens6, de Saclay, 91191 Gif-sur-Yvette, France accepted in final October Imbert(~), P. d'Etudes Centre Hodges(~), J.A. Laboratory, Los Alamos, National Alamos (RecHved Condens6, Physique de l'Etat et les Moldcules, de Atomes Institut de hybridisation in YbAuCu4 and mettons nous interpr4tons conduction, d'hybridation entre les 41ectrons 4f et les 41ectrons de termes propri4t4s de type 41ectron lourd. L'dchelle d'4ner#e kBTo de l'hybridation estim4e de l'ordre de 0,3 K. Les spectres M6ssbauer dans les phases ordonn4e est et parama- gn4tique pr4sentent des 41argissements de rare inhomog+nes qui sont interpr6t4s en termes de distribution de locales contraintes suivant les axes du cristal, d'4nergie magn4to-41astique comportement compte ce en qui rend des moyenne o,4 K. Abstract. We report on spontaneous sizeable 4f anisotropy of electron The energy ordered arising energy JOURNAL moment DE with and from kBTo scale electron of distribution a PHYSIQUE I of local K. oA T 2, N' 4, APR~ lW2 heavy K), we to that of the is spectroscopy material electron measure magnetic hybridisation, hybridisation paramagnetic phases o.2 respect M6ssbauer cubic the interionic the conduction °Yb a magnetic properties of magnetically ordered phase (TN perature a crystal which the In the antiferro- Yb~+ saturated reduction be o.3 for the K. heavy electron The inhomogeneous line broadenings strains along the ill ii crystal axes, show of the low tem- T7 ground state and we evidence a We interpret these features in terms of accounts to of YbAuCu4. field interaction. estimated $l investigation M6ssbauer which of mean properties. spectra are in the interpreted as magneto-elastic

We determined the crystal-field split Hund's rule ground state of the noncentrosymmetric heavy fermion superconductor ${\text{CePt}}_{3}\text{Si}$ with polarization dependent soft x-ray absorption spectroscopy (XAS) and polarized neutron scattering. We are also able to give the sequence of the crystal-field states from the temperature evolution of the linear dichroic signal in the XAS. The quantitative analysis of the XAS temperature dependence together with the neutron transition energies complete the identification of the crystal-field level scheme.

Static-susceptibility and thermal-expansion measurements indicate that Ce{sub 3}Bi{sub 4}Pt{sub 3} is mixed-valent-like, whereas transport measurements reveal a gap of {Delta}=5 meV in the electronic excitation spectrum. We report the magnetic response of Ce{sub 3}Bi{sub 4}Pt{sub 3}, at temperatures between 2 and 150 K, determined with incident neutron energies of 3.1, 17, and 69 meV. The isostructural, nonmagnetic reference compound La{sub 3}Bi{sub 4}Pt{sub 3} was also studied at the same temperatures and energies so that phonon contributions could be subtracted accurately. At 2 K, a gap {Delta}{sub {ital m}}=12 meV is present in the magnetic excitation spectrum: the 3.1-, 17-, and 69-meV data consistently show that the magnetic intensity is zero for energy transfers less than 12 meV, rises sharply between 12 and 20 meV, and falls off smoothly beyond. Above 50 K, the gap in the spin-spin correlation function starts to fill. The neutron results reproduce the temperature dependence of the bulk susceptibility. The relationship between these and other measurements will be discussed.

Polarized neutron scattering measurements on a single crystal of composition CeIn1Sn2 show a broad, single-ion, spectral response centered on a characteristic energy of approximately 9+/-1 meV at the zone boundary point (0 0 1.5). The zone center spectral response is closely similar in form but has a slightly reduced amplitude, smaller by some 20%. Constant-omega scans show that these intensity modulations, of amplitude approximately 10%, resembling intersite antiferromagnetic correlations, are superimposed on a mean variation that follows the Ce3+, 4f;{1}, single-ion form factor, and are tentatively attributed to q-dependent hybridization of the localized 4f state with the conduction electrons.

We have investigated the dynamic susceptibility χ″( Q , ω) of the alloy system CePd 3− x Ag x (0⩽ x ⩽1) by time-of-flight spectroscopy using neutrons of incident energies of 3.1, 17, 67 and 115 meV and obtain the following principal results: i) we have reconfirmed the broad inelastic hump in CePd 3 centered at about 50 meV observed previously and varified that this contains most of the magnetic spectral weight, ii) we observed an inhomogeneous magnetic response for the system CePd 3− x Ag x composed of two inelastic humps, and iii) we have identified a narrow quasi-elastic contribution having an energy width of less than 2 meV which increases in intensity and decreases in width with increasing Ag-concentration.

We infer that soft-x-ray absorption spectroscopy is a versatile method for the determination of the crystal-field ground state symmetry of rare earth heavy fermion systems, complementing neutron scattering. Using realistic and universal parameters, we provide a theoretical mapping between the polarization dependence of Ce ${M}_{4,5}$ spectra and the charge distribution of the Ce $4f$ states. The experimental resolution can be orders of magnitude larger than the $4f$ crystal-field splitting itself. To demonstrate the experimental feasibility of the method, we investigated ${\mathrm{CePd}}_{2}{\mathrm{Si}}_{2}$, thereby settling an existing disagreement about its crystal-field ground state.

We have studied the thermal conductivity $\ensuremath{\kappa}$ on single crystalline samples of the antiferromagnetic monolayer cuprates ${R}_{2}\mathrm{Cu}{\mathrm{O}}_{4}$ with $R=\mathrm{La}$, Pr, Nd, Sm, Eu, and Gd. For a heat current within the $\mathrm{Cu}{\mathrm{O}}_{2}$ planes, i.e., for ${\ensuremath{\kappa}}_{ab}$ we find high-temperature anomalies around $250\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in all samples. In contrast, the thermal conductivity ${\ensuremath{\kappa}}_{c}$ perpendicular to the $\mathrm{Cu}{\mathrm{O}}_{2}$ planes, which we measured for $R=\mathrm{La}$, Pr, and Gd, shows a conventional temperature dependence as expected for a purely phononic thermal conductivity. This qualitative anisotropy of ${\ensuremath{\kappa}}_{i}$ and the anomalous temperature dependence of ${\ensuremath{\kappa}}_{ab}$ give evidence for a significant magnetic contribution ${\ensuremath{\kappa}}_{\mathrm{mag}}$ to the heat transport within the $\mathrm{Cu}{\mathrm{O}}_{2}$ planes. Our results suggest, that a large magnetic contribution to the heat current is a common feature of single-layer cuprates. We find that ${\ensuremath{\kappa}}_{\mathrm{mag}}$ is hardly affected by structural instabilities, whereas already weak charge carrier doping causes a strong suppression of ${\ensuremath{\kappa}}_{\mathrm{mag}}$.

PHYSICA[ Physica B 199&200 (1994) 480-482 ELSEVIER Spin-hole doping in the Kondo insulator Ce Bi4Pt3 studied by neutron scattering A. Severing ~, T. Perring b, J.D. Thompson ~'*, P.C. Canfield ¢'d, Z. Fisk ¢ Institute Laue-Langevin, Grenoble, France bRutherford Laboratory, Rutherford, UK CLos Alamos National Laboratm'y, Los Alamos, N M 87545. USA ~ Ames Laboratory, Ames, IA 50011, USA Abstract Inelastic neutron scattering from (Ce~_ ~La~)3Bi4Pta, with x = 0, 0.1 and 0.25, shows that a gap in the spin excitatio~ spectrum decreases monotonically with increasing x and remains well-defined even for x = 0.25. Although the vast majority of heavy-electron com- pounds are metallic at low temperatures, a few are known to have small semiconducting gaps Eg on the order of tens of Kelvins. A simple interpretation tor the origin of Eg is that the bare 4t - or 5f-energy level is renormalized by many-body interactions to be deger, er- ate with a aroad conduction band with which the rener- malized f-level hybridizes. Provided the electron count, including the strongly interacting f-electrons, is exactly two, the lower hybridized band will be filled and the upper band will be empty, leaving an indirect gap from zone boundary to zone center of order V2/W, where V is the hybridization matrix element and W is the conduc- tion bandwidth [1]. An interesting aspect of this model is that, in addition to the existence of a charge gap, there should also be a gap in the spin excitation spectrum [2, 3]. Experimental confirmation of a spin gap has come from inelastic neutron scattering on Ce3Bi4Pt3 [4] and CeNiSn [5]. In both cases the spin and charge gaps are of comparable magnitude and of order 100 and 10 K for the two compounds, respectively. * Corresponding author. When the f-sublattice periodicity is broken by substitu- ting La for Ce in (Cel-xLax)3Bi4Pta a metallic-like resis- tivity develops, the T-linear specific heat coefficient in- creases from near zero to a large value characteristic, of a weakly mixed-valence compound, and a peak at T = Tmax in the static susceptibility moves to lower tem- peratures [6]. Similar trends have also been reported in Cel - xLaxNiSn [7], Sm 1 - xLaxB6 [8] and Yb I - xLuxB12 [9], and are consistent with the presence of Kondo-like interactions. An important question to be answered is how do these small-gap semiconductors evolve into heavy-electron metals with increasing concentrations of nonmagnetic La or Lu. To address this question we have determined the evolution of the spin gap in (Ce: _ ~La,)3Bi~Pt~ by inelastic neutron scattering experi- rnents. Single crystals of (Cet -,LaxlaBi4Pt3 were grown from a Bi flux with nominal La concentrations x = 0, 0.t, 0.25 and 1.0. Electrical resistance and static susceptibility measurements on these crystals followed systematics re- ported previously [6]. Neutron scattering was performed on tt,e H E T spectrometer at the Rutherford spallation source using incident neutron energies Eo of 30 and 0921-4526/94/$07.00 C) 1994 Elsevier Science B.V. All rights reserved SSDI 0921-4526(93)E0364-M

A polarised neutron experiment with neutron energy analysis has been performed with a single- Q sample of chromium in a large magnetic field. The 4-meV “commensurate” mode is found to involve spin fluctuations parallel to the ordered chromium moments.

An inelastic neutron scattering (INS) study was performed on the heavy fermion system CePtSi. A Kondo temperature of 16 K can be inferred from the quasielastic line width. There are two inelastic lines corresponding to CF-transitions from the ground to the first and second excited state at 6.3 and 17.8meV, respectively.

We have investigated the spin-spin correlations in single crystal CeSn 2 In by inelastic neutron scattering.

The interplay between electronic and magnetic correlations in certain 4f and 5f intermetallic compounds has been shown1 to lead to novel ground state properties, including strongly renormalized effective electron masses, homogeneous mixed valence of the f-configuration and unconventional superconductivity. Whereas the vast majority of these compounds are metallic at low temperatures, a few examples, such as SmB6 (Ref. 2), SmS (Ref. 3), and YbB12 (Ref. 4), have been known for some time to be small-gap semiconductors, with gaps of order 100K. Within the past two or three years several new examples have been discovered, notably in Ce5–8 and U9 compounds, suggesting that small-gap semiconductors may be a general consequence of strongly interacting electrons. With very few exceptions, the crystal structures of these materials are cubic which, as will be argued, is favorable for the appearance of a small gap in the electronic spectrum. Further common features are temperature variations in the cubic lattice parameter, in magnetic susceptibility and in L-edge absorption spectra that are consistent with an unstable f-configuration arising from hybridization between f and ligand electrons. The extent to which the physics of these small-gap semiconductors is similar to metals with otherwise similar properties remains an outstanding question but their analogous behavior to Kondo-lattice metals has led to the terminology Kondo insulators.10,11 In the following we review transport and thermodynamic properties of the small-gap semiconductor Ce3Bi4Pt3 and discuss them in relation to what is known about other Kondo insulators and metals.

The low-energy part ( h ω ≤ 2 meV ) of the magnetic excitations of polycrystalline samples of Nd2−xCexCuO4 with x = 0, 0.16 and 0.20 has been measured with inelastic magnetic neutron scattering between 1.8 and 300 K. All observed magnetic scattering originates from transitions within the ground-state doublet of Nd3+. For Nd2CuO4 the response is inelastic at T = 1.8 K with Q-dependent positions and intensities of two strong and one weak mode. For x = 0.16 and 0.20 the magnetic response is mainly quasi-elastic with some residual inelastic intensity at low-Q values. For the higher temperatures all spectra become quasi-elastic. The shape of the response changes between 40 and 100 K from Gaussian to Lorentzian.

Neutron spectroscopy has been used to study the spin dynamics of alloys in the series CeRu2Si2−xGex is a widely studied heavy-fermion compound, while CeRu2Ge2 is a ferromagnet with Tc = 10 K. The measured quasielastic response is due to longitudinal spin fluctuations of the almost pure |± 5 2 > ground states. The energy widths are found to be strongly wavevector dependent, indicating the importance of intersite correlations. The extrapolated single ion linewidth shows that the strength of the 4f hybridisation decreases with increasing x, with TK ranging from 12 K for x=0.2 to 1.9 K for x = 2.0.

The results of high-resolution inelastic neutron scattering experiments on Ce${X}_{2}$${\mathrm{Si}}_{2}$ (X=Au, Pd, Rh, and Ru) in the temperature interval 1.5--250 K are reported, and the interplay of 4f conduction-electron scattering and magnetic order is discussed. The quasielastic linewidths increase within the series \ensuremath{\Gamma}2(Au)/2(Pd)/2(Rh)/2(Ru), although the N\'eel temperature of ${\mathrm{CeRh}}_{2}$${\mathrm{Si}}_{2}$ is about four times larger than in the Au- and Pd-based compounds. The quasielastic linewidth of the nonordering compound ${\mathrm{CeRu}}_{2}$${\mathrm{Si}}_{2}$ decreases linearly with temperature and converts into an inelastic line when the thermal energy becomes smaller than \ensuremath{\Gamma}/2. An analytic function given by Kuramoto and M\"uller-Hartmann is applied to fit the low-temperature data of ${\mathrm{CeRu}}_{2}$${\mathrm{Si}}_{2}$. In addition, the low-temperature inelastic line in ${\mathrm{CeRu}}_{2}$${\mathrm{Si}}_{2}$ exhibits a strong \ensuremath{\Vert}Q\ensuremath{\Vert} dependence: its inelastic position and linewidth vary with \ensuremath{\Vert}Q\ensuremath{\Vert}. .AE

We report measurements of the phonon dispersion relation in intermediate-valence ${\mathrm{CePd}}_{3}$. The longitudinal-acoustic modes show a distinct softening above 100 K and a temperature-dependent broadening and splitting at higher temperatures. Especially in the 〈100〉 direction the longitudinal modes differ from those of other ${\mathrm{Cu}}_{3}$Au structures. A good fit of the room-temperature dispersion curves is given by a 16-parameter Born\char21{}von K\'arm\'an model with a breathing force as an additional degree of freedom.

We present the results of two types of inelastic neutron scattering experiments on the heavy-fermion system ${\mathrm{CeCu}}_{2\ifmmode\pm\else\textpm\fi{}0.2}$${\mathrm{Si}}_{2}$ to investigate the quasielastic scattering (low-energy response) and the crystal-field (CF) excitations (high-energy response). A characteristic energy width of about 0.7 meV is found for the magnetic low-energy response at low temperatures, and the CF scheme given earlier for ${\mathrm{CeCu}}_{2}$${\mathrm{Si}}_{2}$ is roughly confirmed. The inelastic spectrum of ${\mathrm{CeCu}}_{2.2}$${\mathrm{Si}}_{2}$ gives some indications for a coexistence of \ensuremath{\gamma}-cerium and \ensuremath{\alpha}-cerium. The scattering intensities are compared with static susceptibility measurements.