Electronic structure ofCeRu2X2(X=Si,

Abstract

Soft and hard X-ray photoelectron spectroscopy (PES) has been performed for one of the heavy fermion system CeRu2Si2 and a 4f -localized ferromagnet CeRu2Ge2 in the paramagnetic phase. The three-dimensional band structures and Fermi surface (FS) shapes of CeRu2Si2 have been determined by soft X-ray hν-dependent angle resolved photoelectron spectroscopy (ARPES). The differences in the Fermi surface topology and the non-4f electronic structures between CeRu2Si2 and CeRu2Ge2 are qualitatively explained by the band-structure calculation for both 4f itinerant and localized models, respectively. The Ce valences in CeRu2X2 (X = Si, Ge) at 20 K are quantitatively estimated by the single impurity Anderson model calculation, where the Ce 3d hard X-ray core-level PES and Ce 3d X-ray absorption spectra have shown stronger hybridization and signature for the partial 4f contribution to the conduction electrons in CeRu2Si2.

Fermi Surface Properties, Metamagnetic Transition and Quantum Phase Transition of CeRu2Si2 and Its Alloys Probed by the dHvA Effect

“…The present observation for temperature variation is in contrast with those in the heavy fermion compounds where no observation of an intermediate Fermi surface between those corresponding to the large Fermi surface and the small Fermi surface has been reported from ARPES measurements. [112][113][114][115]184 It is also reported in UPd 2 Al 3 that the Fermi surface changes rather abruptly between 40 K and 60 K. 184 Then, the continuous change in the observed frequency may not directly correspond to a continuous change of the Fermi edge with temperature. But it could be explained by the two Fermi edges corresponding to the small and large Fermi surfaces and the former one diminishes while the latter one grows with decreasing temperature as expected in the case of compounds.…”

Magnetic behavior near the boundary of4fdelocalization in ferromagnetic CeRu2Ge2and paramagnetic CeRu

“…2, the line shapes of the XAS and the XMCD spectra are almost identical to the results in the previous works. 19,27,28,34 Figure 3 demonstrates the magnetic field dependencies of the intensity of the dominant XMCD peak at the M 4 edge of CeRu 2 Ge 2 and CeRu 2 Si 2 . The data of CeRu 2 Ge 2 at 5.5 K indicates a clear ferromagnetic transition, while a paramagnetic linear dependence is observed at 20 K. A metamagnetic transition at H M ≈ 7.7 T is unclear in the data of CeRu 2 Si 2 at 4.6 K, since clear transition would be observed at the temperature below 2 K. 25 However, the difference between 4.6 and 10 K demonstrates that a trace of the metamagnetic transition appears as a slight hump at around 7.7 T, and thus the metamagnetic transition can be tracked even at the temperature of 4.6 K. The upturn of the difference in the range 0-4 T is understood as a temperature dependence of Brillouin function.…”

“…[13][14][15] The itinerant nature of the Ce 4f electrons below T K is suggested from a comparison of the Fermi surfaces between the experimental (dHvA and ARPES) and the theoretical results. [16][17][18][19][20][21][22][23][24] On the other hand, CeRu 2 Si 2 shows a metamagnetic transition above the critical field H M ≈ 7.7 T along the [001] direction, 25,26 indicating that CeRu 2 Si 2 is located near the boundary of an emergence of magnetic order or the boundary of 4f localization.…”

Electronic Structures of Ferromagnetic CeAgSb2: Soft X-ray Absorption, Magnetic Circular Dichroism, and Angle-Resolved Photoemission Spectroscopies

“…Moreover, it is well known that the conventional low energy ARPES probes only the surface electronic structures which is often quite different from the bulk ones especially for the strongly correlated 4f electron systems [15][16][17] . In contrast, the soft X-ray ARPES is more sensitive to the bulk electronic structure with still reasonable momentum resolution [18][19][20] .…”