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

Abstract

We report a combined study for the electronic structures of ferromagnetic CeAgSb2 using soft X-ray absorption (XAS), magnetic circular dichroism (XMCD), and angle-resolved photoemission (ARPES) spectroscopies. The Ce M4,5 XAS spectra show very small satellite structures, reflecting a strongly localized character of the Ce 4f electrons. The linear dichroism effects in the Ce M4,5 XAS spectra demonstrate the ground state Ce 4f symmetry of Γ6, the spatial distribution of which is directed along the c-axis. The XMCD results give support to the picture of local-moment magnetism in CeAgSb2. Moreover it is also found that the theoretical band dispersions for LaAgSb2 provides better description of the ARPES band structures than those for CeAgSb2. Nevertheless, ARPES spectra at the Ce 3d-4f resonance show the momentum dependence for the intensity ratio between Ce 4f 1 5/2 and 4f 1 7/2 peaks in a part of the Brillouin zone, suggesting the non-negligible momentum dependent hybridization effect between the Ce 4f and the conduction electrons. This is associated with the moderate mass enhancement in CeAgSb2.

Evidence for momentum-dependent heavy-fermionic electronic structures: Soft x-ray ARPES for the superconductor CeNi2Ge2 in the normal state

“…The lack of microscopic experimental information makes it difficult to reveal the origin of the quantum criticality for realistic HF systems, which is proposed on the basis of several models due to the spin fluctuation [25], Kondo breakdown [26][27][28], and valence fluctuation theories [29,30]. The HF phenomena are complicated by the strong momentum dependence of a HF nature arising from anisotropic cf hybridizations, which reflect the 4f charge distributions as clearly revealed by soft x-ray absorption spectroscopy [31][32][33]. To tackle this problem, it is essential to seriously investigate the band structures along various directions in three-dimensional (3D) reciprocal space.…”

Ground State Local 4f Symmetry of CeAgSb2 Probed by Linearly Polarized Hard X-ray Photoemission

“…The Sommerfeld coefficient of γ is 46 mJ/(mol•K 2 ), which gives the moderate mass enhancement factor of 21 for LaAgSb 2 [4]. The soft X-ray angle resolved photoemission experiments reported that the Ce 4 f states were almost localized and the experimental band structures are well explained by the band structure calculation for LaAgSb 2 [5], suggesting that the electronic structure is basically described as Ce 3+ ionic picture.…”

“…The anisotropy parameter α 2 along the c-axis of the Γ 7 states can be determined by linearly polarized X-ray absorption spectroscopy (XAS) [5][6][7][8]. However, it is insensitive for the in-plane rotational symmetry, which is described by the ± sign of the linear combination of the |± 5 2 ⟩ and |± 3 2 ⟩ states, due to the fundamental limitation of the dipole selection rule in the tetragonal systems.…”

“…The anisotropy parameter α 2 along the c-axis of the Γ 7 states can be determined by linearly polarized X-ray absorption spectroscopy (XAS) [5][6][7][8]. However, it is insensitive for the in-plane rotational symmetry, which is described by the ± sign of the linear combination of the |± 5 2 ⟩ and |± 3 2 ⟩ states, due to the fundamental limitation of the dipole selection rule in the tetragonal systems. This problem has been overcome by the linearly polarized angle-resolved hard X-ray photoemission (HAXPES) with an additional parameter of the detection direction of the photoelectrons [9][10][11][12][13][14].…”

“…. This motivates us to probe the ground state 4 f symmetry of CeAgSb 2 by HAXPES, whose ground states were reported as the Γ 6 symmetry [5]. In this study, we have performed linearly polarized HAXPES for CeAgSb 2 in the paramagnetic phase to establish the HAXPES as a probe of the GS symmetry of the tetragonal Ce systems.…”