Resonant Inverse Photoemission Research Articles

X-ray Absorption and Inverse Photoemission Study of Y1-xCaxTiO3

We have performed the O 1 s x-ray absorption (XAS) and resonant inverse photoemission spectroscopy (RIPES) in Mott insulator YTiO 3 , band insulator CaTiO 3 and Y 0.61 Ca 0.39 TiO 3 with a metal–in...

Unoccupied Electronic State at Low Temperature of SrTiO3-delta Probed by Resonant Inverse Photoemission Spectroscopy

Unoccupied Electronic State at Low Temperature of SrTiO3-delta Probed by Resonant Inverse Photoemission Spectroscopy

Resonant inverse photoemission of Pr compounds

The resonant inverse photoemission study of Pr metal, PrAl 2 and PrFe 4P 12 was performed in the Pr 4d–4f excitation region. The Pr 4f spectra strongly depend on the excitation energy due to the resonant effect and have two broad peaks originated from f 3 final states. The intensity of the shoulder in the vicinity of the Fermi energy for PrFe 4P 12, which mainly contains f 2 final states on the analogy of the Ce 4f spectra, is much stronger than that for Pr metal and PrAl 2 due to the strong hybridization between Pr 4f electrons and valence-band electrons in PrFe 4P 12. This result is consistent with the conclusion derived from the photoemission spectroscopy.

Conduction band satellite of Ni metal observed using 3p-3d resonant inverse photoemission study

Resonant inverse photoemission spectra of Ni metal have been obtained across the Ni 3$p$ absorption edge. The intensity of Ni 3$d$ band just above Fermi edge shows asymmetric Fano-like resonance. Satellite structures are found at about 2.5 and 4.2 eV above Fermi edge, which show resonant enhancement at the absorption edge. The satellite structures are due to a many-body configuration interaction and confirms the existence of 3$d^8$ configuration in the ground state of Ni metal.

Resonant inverse photoemission spectroscopy in soft X-ray region

Resonant inverse photoemission spectroscopy (RIPES) measurements have been performed in the soft X-ray (SX) region. The energy region, which could not be accessible up to these days, includes core levels of many important elements to be investigated. They were applied to transition metals (TM), rare earth (RE) metals, and their compounds. Remarkable resonance enhancement was observed in Ce 4d→4f resonance of some Ce compounds. This gives us complementary information with Ce 3d resonance IPES that was reported before. 2p and 3p resonance spectra were observed for the TM compounds. These resonances show rather weak enhancement compared with those of Ce compounds, although apparent resonance feature was observed. These results are well-reproduced by many-body configuration interaction on the basis of the Anderson impurity model. Though the study has just started, the results demonstrated the effectiveness of the RIPES measurements.

Mn 3p–3d RESONANT INVERSE-PHOTOEMISSION SPECTROSCOPY OF NiAs-TYPE MnTe

Resonant inverse-photoemission spectra of NiAs-type MnTe have been measured with the tunable photon energy mode at kinetic energies of incident electrons (Ek) in the Mn 3p–3d excitation region. The peak structure at 2.9 eV above the valence-band maximum (VBM) is resonantly enhanced at Ek = 50 eV and is attributed to transitions to d 6 final states with 5 E and 5 T 2 symmetries. The broad structure around 12 eV above the VBM in the spectrum at Ek = 46.5 eV and a shoulder on the higher energy side of the main peak at 2.9 eV in the spectrum at Ek = 50 eV is assigned to [Formula: see text] final states and d6 final states with 3Γ symmetries, respectively, where [Formula: see text] stands for a ligand hole and Γ an irreducible representation.

Theoretical and experimental study of surface and bulk contributions in resonant inverse photoemission ofCeRh3

The surface and bulk sensitivity of resonant inverse photoemission (RIPE) spectroscopy is theoretically and experimentally studied for a typical mixed-valent compound ${\mathrm{CeRh}}_{3}$ around the prethreshold region of the Ce ${N}_{4,5}$ edge. The strong resonance effects---the change of the intensity ratio between the ${f}^{1}$ and ${f}^{2}$ structures and the change of the spectral shape in the ${f}^{2}$ structure---are clearly found with the change of the excitation energy. The observed resonance behavior is successfully analyzed with an impurity Anderson model by explicitly considering both bulk and surface contributions in RIPE spectra. The explicit consideration of the surface contribution, in addition to the full-multiplet coupling effects in a Ce ion, is indispensable to reproduce the observed RIPE spectra for the whole excitation energy range around the prethreshold. The RIPE spectra of ${\mathrm{CeRh}}_{3}$ around the giant resonance of the Ce ${N}_{4,5}$ edge are also calculated with explicit consideration of the surface contribution. The present calculation improves our previous one for the Ce ${N}_{4,5}$ RIPE spectra of ${\mathrm{CeRh}}_{3}$ without the surface contribution. Moreover, the RIPE spectra of ${\mathrm{CeRh}}_{3}$ at the Ce ${M}_{5}$ edge are also investigated by considering surface and bulk effects. We emphasize the importance of the surface contribution in the interpretation of the Ce ${M}_{5}$ RIPE spectra.

Resonant inverse photoemission study on strongly correlated systems

Abstract We have performed resonant inverse photoemission (RIPE) spectroscopy on the transition metal and rare-earth metal compounds in the ultraviolet energy region. We present, here, some characteristics of the RIPE spectra of several intermetallic Ce compounds at the Ce-N 4,5 absorption edge. Clear RIPE spectra are observed. From the comparison between the experimental and the calculated spectra, the resonance behaviors can be well explained within the localized picture of the 4f electrons. On the other hand, the information about the fractional 4f occupancy in the systems with high Kondo temperature is strongly reflected in the intensities of the coherent and incoherent components of RIPE spectra. The RIPE spectra sensitively detect the variations in the 4f electronic states by destruction of the collective Kondo state, with increasing temperature. We can derive direct information about the temperature and T K dependence of the 4f electronic states from the spectra. On the other hand, it is necessary to take the surface contributions into account in order to derive quantitative information. We present an example of the analysis of RIPE spectra at N 4,5 pre-threshold, including both contributions from the bulk and surface.

Theory of resonant spectroscopies in nickel, cerium compounds and other systems

Abstract In this paper, we discuss theoretically information about electronic structures in strongly correlated systems obtained from resonant X-ray spectroscopies. From a many-body point of view on the basis of an impurity Anderson model or a cluster model including the intra-atomic multipole interaction between electrons, we calculate spectra by exactly diagonalizing our Hamiltonian. First, for ferromagnetic Ni, through an analysis of magnetic circular dichroism in 3 d resonant photoemission spectroscopy (RPES) and resonant inverse photoemission spectroscopy (RIPES), it is shown that, in addition to 3 d 9 and 3 d 10 , the 3 d 8 configuration with weight of about 20% is contained as electron configuration of a Ni atom in Ni metal. The 3 d 8 configuration is furthermore shown to be mainly composed of 3 F and its relation to the origin of ferromagnetism is discussed. Second, for mixed valent Ce compounds, including CeNi 2 , it is shown, through an analysis of RIPES, tht the 4 f -conduction band hybridization must be reduced by the presence of a core hole. Third, for some 3 d transition metal (TM) oxides, 3 d RPES at TM ion 2 p threshold is shown to be a powerful method for estimating the magnitude of 3 d –3 d interaction strength and the charge transfer energy.

Spin-resolved APS for K-, L- and M-line emissions of Ni

Abstract Appearance potential spectroscopy (APS) spectra are measured near 1s, 2p and 3p core electron excitation energies for ferromagnetic Ni with spin polarized electrons. Spin resolved spectra for Ni 2p 3/2 were explained by a one-electron approximation with parameterized Auger matrix elements. Though the aspects of spin integrated spectra for 2p 1/2 are very similar to those for 2p 3/2 , our spin resolved spectra cannot be explained by the above approximation. The spectra for 1s were measured for Kα characteristic X-ray energy region. Nevertheless they do not show a clear variation of the primary electron spin dependence near 1s appearance potential. The spectra for 3p show an entirely different aspect from those for 2p. This may be caused by the many body effect for which the soft X-ray emission intensity is resonantly enhanced (i.e. resonant inverse photoemission).

Ultrahigh-resolution photoemission and resonant-inverse photoemission spectroscopy on CePd3

Abstract We carried out ultrahigh-resolution photoemission (URPE) and resonant-inverse photoemission spectroscopy on CePd3 and CePd2.9Cu0.1 compounds. The URPE spectra of CePd3 and CePd2.9Cu0.1 clearly show small humps in the vicinity of Fermi level well below the Kondo temperature. The hump is gradually formed below the characteristic coherent temperature T*. We conclude that it gives direct evidence of the appearance of the small pseudogap below T* in CePd3 and CePd2.9Cu0.1.

Resonant inverse photoemission spectroscopy at the prethreshold of theCe−N4,5absorption edge inCePd3

We performed the resonant inverse photoemission (RIPE) study on ${\mathrm{CePd}}_{3}$ at the prethreshold region of the $\mathrm{Ce}{\ensuremath{-}N}_{4,5}$ absorption edge. The surface effects on RIPE spectra are discussed through the investigation of the resonance behaviors. Comparison between the RIPE spectra and the calculated resonant-excitation probability of the intermediate states indicates the existence of specific excitation energy range, where a strong resonant enhancement occurs for the bulk or the surface $4f$ spectrum.

Resonant inverse photoemission study of CeCoGe 3− xSi x

We have measured the resonant inverse photoemission spectra (RIPES) of CeCoGe 3−x Si x (0⩽x⩽3) as functions of composition and temperature. The strong composition dependence of 4f-state just above the Fermi level ( E F) shows that the localized 4f electrons in the compound become itinerant due to the enhanced Kondo effect. Temperature dependence of the f 1-peak indicates a transition from the paramagnetic state at room temperature to a coherent Fermi-liquid regime at low temperatures. The most remarkable variation of the spectra has been observed above 200 K with increasing temperature in CeCoSi 3 which has a very high Kondo temperature T K of about 900 K. This suggests that the change in the 4f-electronic state of CeCoSi 3 may be scaled by the coherence transition temperature rather than T K.

Observation of the coherence transition into a collective dense Kondo state by resonant inverse photoemission spectroscopy

By the resonant inverse photoemission spectroscopy (RIPES), we study the crossover from mixed-valent to heavy-fermion and Kondo regime in ${\mathrm{CeCoGe}}_{3\ensuremath{-}x}{\mathrm{Si}}_{x}$ $(0<~x<~3).$ We have measured the RIPE spectra as functions of composition and temperature. The strong composition dependence of $4f$ state (``${f}^{1}$ peak'') just above the Fermi level shows that the localized $4f$ electrons in the compound become itinerant due to the enhanced Kondo effect within the range $1.0<~x<~1.5.$ Temperature dependence of the ${f}^{1}$ peak indicates a transition from the paramagnetic state at room temperature to a coherent Fermi-liquid regime at low temperatures where the Kondo effect dominates. The most remarkable variation of the spectra has been observed above 200 K with increasing temperature in ${\mathrm{CeCoSi}}_{3}$ which has a very high Kondo temperature ${T}_{K}$ of about 900 K. This suggests that the change in the $4f$-electronic state of ${\mathrm{CeCoSi}}_{3}$ may be scaled by the coherence transition temperature rather than ${T}_{K}.$

Resonance effect on inverse-photoemission spectroscopy ofCeRh3,CePd3,andCeSn3

The resonant inverse photoemission study (RIPES) at the Ce $4\stackrel{\ensuremath{\rightarrow}}{d}4f$ absorption edge of ${\mathrm{CeRh}}_{3},$ ${\mathrm{CePd}}_{3},$ and ${\mathrm{CeSn}}_{3}$ has been carried out. The RIPES spectra show the wide variety of the $4f$ electron character in these compounds, indicating the characteristic Kondo temperature and $4f$ electron number. The excitation energy dependence of $4f$-spectral resonance, especially in ${4f}^{2}$ final-state structure, indicates a large $4d\ensuremath{-}4f$ multiplet splitting and strict selection rule in the final state of the RIPES process. Constant final-state spectra of the ${f}^{1}$ final state show the $4f$ spin-orbit splitting components. A calculation is carried out by the impurity Anderson model with full multiplet effects and explains well the excitation energy dependence of the RIPES spectra.

Resonant inverse photoemission in 4f systems

Resonant inverse photoemission spectroscopy (RIPES) is a new spectroscopic probe of the electronic states in solids. It exploits the resonant enhancement of the inverse photoemission cross section occurring at appropriate core absorption edges, and is therefore the counterpart of resonant photoemission for the unoccupied states. We present the results of a RIPES investigation of cerium-based Kondo systems, which illustrate the main aspects of the technique, and briefly review some recent developments involving these and other systems. (C) 1999 Elsevier Science B.V. All rights reserved.

Contrasting Kondo behavior and resonant inverse photoemission spectra of CeTSi 3 and CeTGe 3 (T=Rh and Ir)

CeTSi 3 and CeTGe 3 (T=Rh and Ir) were investigated by measuring the magnetic susceptibility, specific heat, electrical resistivity, the resonant inverse photoemission (RIPES) and M IV,V X-ray absorption spectra (XAS). The germanides showed a very weak Kondo effect, but the silicides exhibited a negatively large Weiss temperature (≈−130 K) and a ln T dependence of magnetic resistivity above 100 K, suggesting that they are Kondo-lattice compounds with a high Kondo temperature T K (≈100 K). The Curie–Weiss law suggests that Ce atoms in these compounds remain close to 3+ down to about 150 K in spite of their high T K. Both RIPES and M IV,V XAS support their apparently stable valency.

Resonant inverse photoemission study on CeRh 3 at Ce 4d absorption edge

The resonant inverse photoemission study (RIPES) of CeRh 3 has been carried out at Ce 4d→4f absorption edge. The 4f cross section increases drastically when the excitation energy is tuned to absorption edge. The line shape of 4f 2 state changes by the resonance effect because of its multiplet structure. The RIPES of CeRh 3 which is in the valence fluctuation (VF) region shows the strong f 1 intensity. The energy position of f 1 peak of CeRd 3 is about 1 eV, which reflects the extremely high Kondo temperature of CeRh 3.

Resonant inverse photoemission study of NiS2−xSex

Resonant inverse photoemission (RIPES) spectra of NiS 2− x Se x were measured. Two structures are observed at about 1.6 and 2.6 eV above Fermi energy. It was found that the structure at about 1.6 eV decreases its intensity with the resonance. As x increases from 0.45 to 0.85, the intensity of the structure just above the Fermi energy increases and shifts close to the Fermi energy, so that the Fermi edge intensity increases in IPES spectra.

Intersite charge transfer effects on resonant inverse photoemission of Ni compounds

Abstract We investigate inter-transition-metal-ion-site charge transfer effects on the resonant inverse photoemission at the Ni 2p threshold in NiO and NiS, using Ni2X11 (X=O, S) cluster model taking into account full degeneracy of the 3d orbitals and their intraatomic multipole interaction. In addition to the resonant process 3d8→2p3d10→3d9, which is also expected from models with single Ni ion site, there are other resonant processes 3d7→2p3d9→3d8 and 3d8 L →2p3d10 L →3d9 L starting from the 3d7 and 3d8 L configurations arising from the intersite charge transfer in the initial state, i.e. transfer of an electron to the neighboring Ni site. The incidence angle dependence of the spectra is also discussed and it is shown that the spectra exhibit a strong incidence angle dependence.