Core and shallow-cored- tof-shell excitations in rare-earth metals

Abstract

We report on the results of probing the light lanthanide metals Ce, Pr, and Nd with inelastic x-ray and electron scattering. Transmission electron microscope-based electron spectroscopy and nonresonant inelastic x-ray scattering are shown to be in a high degree of accord, and here serve as complementary probes of electronic structure. The high resolution and high signal-to-noise electron technique allows for the measurement of the complex and subtle excitation spectra in the lanthanide metals, validating the applicability of the screened trivalent atomic model used for these materials. In addition, the momentum transfer dependence of the x-ray scattering is extracted and compared against atomic calculations for the most tightly bound excitonic resonances, which provides a direct test of the predicted atomic radial wave functions.

Determining the In-Plane Orientation of the Ground-State Orbital ofCeCu2Si2

“…For rare-earth materials, higher multipole 4d ! 4f core level excitations (N 4;5 edge) have been observed for large momentum transfers jqj by Gordon et al [10,16] and Bradley et al [15]. It was actually demonstrated experimentally how the dipole signal decreases with increasing jqj while dipole forbidden transitions appear.…”

“…In this work we therefore utilize the higher than dipole transitions in nonresonant inelastic x-ray scattering (NIXS) [8][9][10][11][12][13][14][15][16][17][18] and introduce it as a spectroscopic tool new to this research field of heavy-fermion physics. We will show below that we can resolve reliably the so far unknown orientation of the ground-state orbital in the archetype system CeCu 2 Si 2 , which was the first heavy-fermion compound where unconventional superconductivity was discovered more than 30 years ago [19].…”

“…NIXS has became feasible thanks to the high brilliance of modern synchrotrons and advanced instrumentation and has developed into a rapidly growing field providing complementary means to x-ray absorption methods in the study of core level excitations, and also offering the possibility to go beyond the dipole limits [8][9][10][11][12][13][14][15][16][17][18]. For rare-earth materials, higher multipole 4d !…”

A high resolution and large solid angle x-ray Raman spectroscopy end-station at the Stanford Synchrotron Radiation Lightsource

“…Further on, the high energy resolution of the end station (∼ 270 meV at low-q) could also render the present end-station as a powerful tool to reveal new insights related to low-energy non-dipole transitions in atoms and molecular systems through q-dependent studies within the low-q regime. [50][51][52][53][54][55][56][57][58] Moreover, XRS from semicore levels of heavy elements studied with the present instrument will give improved resolution of the overlapping multiplet featuresan important improvement for broader application of XRS to f-electron systems. [59][60][61][62] The continuous progress with the x-ray optics as well as the availability of modern undulator radiation beamlines, such as the anticipated new undulator beamline at SSRL dedicated to high resolution x-ray spectroscopy, will further boost this technique to a wide range of applications.…”

Inelastic X-ray Scattering Studies of Electronic Excitations

“…One of the applications of XRS in strongly correlated electron systems is the excitation from a shallow core level, which is equivalent to the soft x-ray absorption. For example, the absorption spectra at the M 2;3 -edges (3p-3d) of transition metals, 66) the N 4;5 -edges (4d-4f ) of rare-earth elements, [66][67][68][69] and at the O 4;5 -edges (5d-5f ) of actinide elements 70,71) have been studied. Compared with conventional x-ray absorption spectroscopy, NIXS using hard x-rays has an advantage of bulk sensitivity and one can extend the measurement under extreme conditions such as high pressure.…”