Determining the Crystal-Field Ground State in Rare Earth Heavy Fermion Materials Using Soft-X-Ray Absorption Spectroscopy

Abstract

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 CePd2Si2, thereby settling an existing disagreement about its crystal-field ground state.

Non-Fermi liquid regimes with and without quantum criticality in Ce 1− x Yb x CoIn 5

“…Therefore, we conclude that for H < H QCP the conduction electrons are only weakly coupled to the local spins (i.e., there is a small amount of admixture between the f-electron and the conduction-electron states). However, for H > H QCP , given that the values of 1.3 and 1.0 are only slightly larger then the value of g ≈ 0:83 for the crystal field configuration of Ce ions (27), the conduction states are strongly hybridized with the f states because the AFM fluctuations between the local moments are suppressed, which is reflected in the reduction in the value of the g factor (28). The change in the value of g at H QCP can be interpreted using the phenomenological theory of "Kondo breakdown" at H QCP (28).…”

Exploring small energy scales with x-ray absorption and dichroism

“…Its magnetic variants, x-ray magnetic linear and circular dichroism (XMLD, XMCD) constitute sensitive element and orbital specific probes of magnetic polarization and anisotropy [15][16][17][18][19][20]. XMCD was successfully utilized to reveal the presence of magnetic Kondo screening in CePt 5 /Pt(111) [21].In the present letter we demonstrate that the combined use of linear and magnetic circular dichroism allows us to determine the crystal field structure without recourse to e. g. inelastic neutron scattering, as in some previous work [7][8][9]. Our chosen example of an ultrathin Ce-Ag surface intermetallic furthermore highlights a threefold advantage of this approach.…”

“…In the present letter we demonstrate that the combined use of linear and magnetic circular dichroism allows us to determine the crystal field structure without recourse to e. g. inelastic neutron scattering, as in some previous work [7][8][9] the same installation and therefore can be performed in situ within a single experimental run. Second, the splittings turn out to be of the order of 1 meV only, making their discrimination from quasi-elastic scattering a difficult task.…”

“…It is a fundamental property of hexagonal crystal fields (CF) to split the atomic Ce 4f 1 configuration (j = 5/2) into three Kramers doublets of pure m j character. Unlike in cubic or tetragonal symmetry [7,11,12] the CF is therefore fully specified by |m j level splittings and ordering. We denote the CF splittings as ∆ 1 = E 3/2 −E 1/2 and ∆ 2 = E 5/2 −E 1/2 and determine their magnitude and sign from linear and magnetic circular dichroism measurements at the soft x-ray Ce M 4,5 edges in what follows.…”

“…In a solid environment, the degeneracy of the rare earth 4f ground configuration is lifted by the crystal field in general, causing both an anisotropic 4f charge distribution and, in conjunction with spin orbit coupling, (single ion) magnetic anisotropy. Unraveling the crystal field induced level structure thus constitutes an essential part of understanding the low temperature physics and of establishing correlations between local 4f symmetry at low temperature on the one hand and macroscopic ground state properties on the other.In this respect, the usefulness of probing the 4f configuration with linear polarized soft x-rays [6] has been demonstrated for a variety of Ce compounds in recent years [7][8][9][10][11][12][13][14], allowing to settle several open issues, where other experiments left room for diverging interpretations. Its magnetic variants, x-ray magnetic linear and circular dichroism (XMLD, XMCD) constitute sensitive element and orbital specific probes of magnetic polarization and anisotropy [15][16][17][18][19][20].…”