Probing bulk states of correlated electron systems by high-resolution resonance photoemission

Abstract

Electron correlations are known to play an important role in determining the unusual physical properties of a variety of compounds. Such properties include high-temperature superconductivity, heavy fermion behaviour and metal-to-insulator transitions. High-resolution photoelectron spectroscopy (PES) provides a means of directly probing the electronic states (particularly those near the Fermi level) in these materials, but the short photoelectron mean free paths (< or = 5 A) associated with the low excitation energies conventionally used (< or = 120 eV) make this a surface-sensitive technique. Now that high-resolution PES is possible at much higher energies, with mean free paths as long as 15 A (ref. 6), it should become feasible to probe the bulk electronic states in these materials. Here we demonstrate the power of this technique by applying it to the cerium compounds CeRu2Si2 and CeRu2. Previous PES studies of these compounds revealed very similar spectra for the Ce 4f electronic states, yet it is expected that such states should be different owing to their differing degrees of hybridization with other valence bands. Our determination of the bulk Ce 4f electronic states of these compounds resolves these differences.

Electronic-structure investigation ofCeB6by means of soft-x-ray scattering

“…Since the weight of the f 1 configuration dominates in the ground state of CeB 6 , the normal fluorescence intensity is mainly due to decays through the 3d 9 4 f 1 →3d 10 4 f 0 transitions, where the final states have one electron less than in the ground state. The elastic peak, also referred to as Rayleigh scattering, is due to the 3d 9 4 f 2 →3d 10 4 f 1 transitions back to the ground state.…”

“…1. The XAS spectrum in the upper panel is made up of the hybridized 3d 9 4 f 1 , 3d 9 4 f 2 , and 3d 9 4 f 3 manifolds, where the 3d 9 4 f 2 configuration dominates. The RIXS calculations, shown in the lower panel, are in good agreement with the experimental data in Fig.…”

“…[6][7][8] Recent improvements in the energy resolution of valence-band photoemission spectra with excitation by high-brilliance undulator radiation allow detailed observations of the tail of the so-called Kondo resonance as a very narrow peak in the vicinity of the Fermi level of rather hybridized compounds. 9 However, the predominant surface sensitivity constitutes a serious inherent problem with the use of electron spectroscopies for these kind of studies. Since the 4 f states in the Kondo resonance in the surface are very different from those in the bulk, the SIAM approach for RPES has been a subject of controversy.…”

Electronic structure ofCeRu2X2(X=Si,Yano1, Sekiyama2, Fujiwara3 et al. 2008Phys. Rev. BSelf Cite505210View full textAdd to dashboardCite

“…However, the bulk sensitivity of the soft X-ray (hν ∼ 800 eV) PES was confirmed by the observation of the 4f PES for Ce compounds. 20 Soft X-ray PES is currently an essential approach to reveal electronic states of transition metal compounds 21,22 and rare earth compounds. 23 In addition, more bulk-sensitive PES by using hard X rays (HAXPES) has become feasible.…”

Itinerant U5fband states in the layered compoundUFeGa5observed by soft x-ray angle-resolved photoemission spectroscopy

“…In these works, the experiments were done with low photon energies (hν = 20 − 120 eV). The photoemission experiments performed in this photon energy range 2 are the most surface-sensitive, and may be difficult to relate the observed f band structure to their bulk properties [5]. Especially, U 5f states should be very sensitive to the surface effects [6].…”