Electronic Band Structure of Gd: A Consistent Description

Abstract

The dispersion of the Gd ͑5d6s͒-valence bands has been investigated by means of spin-and angleresolved photoemission. The spin analysis of various spectral features shows that their weak dispersion and unusual broadening is due to the photoelectron lifetime rather than to correlation induced band narrowing as previously proposed. These results resolve a long-standing discrepancy between theoretical and experimental descriptions of the rare earth band structure. DOI: 10.1103/PhysRevLett.86.2846 The unique electronic and magnetic properties of lanthanides result from the coexistence of both highly localized and delocalized levels in the valence region. While the 4f electrons maintain an atomic character in these metals, the (5d6s) states form the metallic bonding and mediate the indirect exchange interaction among the 4f moments.Photoemission spectroscopy gives direct access to the excited-and ground-state configurations of the 4f shell that are indeed well understood for the lanthanide metals [1]. On the contrary, no satisfactory picture of the (5d6s) states exists so far. Even fundamental questions such as the accuracy of the band structure methods for the ground-state description or the influence of many-body effects on the excitation spectra have not yet found an answer. In fact, band structure calculations based on the local spin density approximations (LSDA) predict a large bandwidth for the (5d6s) states in rare earths similar to that of the preceding elements (alkali and alkaline earth metals) in the Periodic Table. These latter cases [2-5] exhibit strongly dispersive photoemission features that are reasonably well interpreted within the paradigms based on effective single-particle approximations, although a quantitative description requires detailed consideration of many-body effects. In sharp contrast, angle-resolved photoemission from lanthanides does not display the expected dispersive behavior of the (5d6s)-bulk states. Various observations [6][7][8] seem to indicate a failure of the effective singleparticle descriptions to the (5d6s) photoemission and suggest the importance of correlation effects.The situation is well illustrated by the case of Gd, which is the most extensively studied lanthanide element for its importance as a prototypical Heisenberg ferromagnet (T C 293 K). Photoemission studies report the energy separations between the G 4 2 2 G 1 1 points [9] and G 4 2 2 A 1 points [8] to be by about a factor of 2 smaller than that predicted by the state-of-the-art calculations [10,11] [shown in Fig. 1(a) for the ferromagnetic ground state [12] ]. Correspondingly, only a significantly weak energy dispersion of the D 2 band is observed by varying the photon energy [8,9]. While this latter observation, separately taken, could possibly be explained by momentum broadening [2], the concomitant discrepancy between the experimental and theoretical bandwidth leads to attribute [8] both the effects to strong electron-electron interactions. Notably, such band narrowing in Gd appears to be much larger than ...

Electronic band structure and Fermi surface of ferromagnetic Tb: Experiment and theory

“…A comparison of the spin splitting in theory and experiment can be found in Ref. 8 for Gd. Summarizing these results, reasonable agreement between calculations and measurement was found, so we are confident that our calculations give a good description of future measurements along the ⌫A line.…”

“…Since this magnetic interaction is highly sensitive to the specific properties of the FS, minor differences of the electronic structure and of the FS in the various lanthanide metals lead to a great variety of magnetic behavior, such as the development of paramagnetic, ferromagnetic, helical antiferromagnetic ͑AFM͒, and conical ferrimagnetic phases, depending on temperature and on the particular lanthanide metal. 4 Many of the experimental and theoretical studies on the relationship between magnetic order and electronic structure of lanthanides focus on Gd metal, [5][6][7][8][9][10][11][12][13] which represents a prototypical local-moment Heisenberg ferromagnet. Some studies also deal with Tb, Dy, and Ho metals.…”

Novel Sb Induced Reconstruction of the (113) Surface of Ge

“…The magnetic moment in these systems primarily originates from the unfilled 4f subshell, which displays a simple spin-mixing behavior due to its atomiclike character. The magnetic coupling between the 4f moments occurs via the highly delocalized (5d6s)-valence states [6]. Various investigations by spin-integrated photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES) report that the exchange splitting of the bulk valence bands vanishes at T C [7][8][9][10][11].…”

“…Experiments were carried out at normal emission with 34 eV photon energy, in order to minimize the spectral broadening effect due to the photoelectron lifetime [6]. The spin polarization was measured by means of a Mott detector operating at 167205-1 0031-9007͞02͞ 88(16)͞167205(4)$20.00…”

“…Experiments were carried out at normal emission with 34 eV photon energy, in order to minimize the spectral broadening effect due to the photoelectron lifetime [6] 100 keV and resolution 160 meV. Thirty monolayer (ML) thick Gd(0001) films were epitaxially grown by e-beam evaporation on a clean W(110) surface at room temperature (P , 2 3 10 210 mbar) and subsequently annealed at 600 K. The cleanliness and crystalline structure of the samples were confirmed by the negligible intensities of impurity-related features in PES and by sharp LEED patterns, respectively.…”