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-based materials; A View on valence-fluctuating EuIr
SiUsachov, D. Yu*; Tarasov, A. V.*; Schulz, S.*; Bokai, K. A.*; Tupitsyn, I. I.*; Poelchen, G.*; Seiro, S.*; Caroca-Canales, N.*; Kliemt, K.*; Mende, M.*; et al.
Physical Review B, 102(20), p.205102_1 - 205102_11, 2020/11
被引用回数：9 パーセンタイル：58.32(Materials Science, Multidisciplinary)Using photoelectron diffraction (PED) and magnetic dichroism measurements, we explore the electronic and magnetic properties of the near-surface region of the valence-fluctuating material EuIrSi. We present and discuss the methodology for modeling of the 4 photoemission spectra, PED patterns and magnetic dichroism for rare-earth-based materials. For the Eu-terminated surface we found that the topmost Eu layer is divalent and exhibits a ferromagnetic order below 10 K. The valency of the next Eu layer, that is the 5th atomic layer, is about 2.8 at low temperature that is close to the valency in the bulk. The properties of the Si-terminated surface are drastically different. The first subsurface Eu layer (4th atomic layer below the surface) behaves divalently and orders ferromagnetically at much higher temperature. Experimental data indicate, however, that there is an admixture of trivalent Eu in this layer, resulting in its valency of about 2.1. The next deeper lying Eu layer (8th atomic layer below the surface) behaves mixed-valently, but the estimated valency of 2.4 is notably lower than the value in the bulk. The obtained results create a background for further studies of exotic surface properties of 4-based materials, and allow to derive information related to valency and magnetism of individual rare-earth layers in a rather extended area near the surface.
Si as a reference for the Luttinger theorem and antiferromagnetism in trivalent heavy-fermion YbRhSiG
ttler, M.*; Generalov, A.*; 藤森 伸一; Kummer, K.*; Chikina, A.*; Seiro, S.*; Danzenb
cher, S.*; Koroteev, Yu. M.*; Chulkov, E. V.*; Radovic, M.*; et al.
Nature Communications (Internet), 10, p.796_1 - 796_7, 2019/02
被引用回数：9 パーセンタイル：62.19(Multidisciplinary Sciences)Application of the Luttinger Theorem (LT) to the canonical heavy-fermion Kondo Lattice (KL) material YbRhSi suggests that its large 4f-derived Fermi surface (FS) in the paramagnetic (PM) regime should be similar in shape and volume to that of the divalent local moment anti-ferromagnet (AFM) EuRhSi in its PM regime. This leads to the tempting opportunity to explore a new experimental realization of the LT in general and how the large FS may change upon the AFM transition below 70 mK in YbRhSi in particular. A detailed knowledge of the FS reconstruction might be essential to disclose the properties of this phase, which is a precursor of quantum criticality and superconductivity. Using angle-resolved photoemission spectroscopy (ARPES), we observe a large FS for PM EuRhSi essentially the same as the one seen in YbRhSi in the KL state at a temperature of 1 K. Across the EuRhSi AFM transition we found an extensive fragmentation of the FS due to Brillouin zone folding, intersection and resulting hybridization of the Doughnut and Jungle gym Fermi-surface sheets. Our results on EuRhSi indicate that the formation of the AFM state in YbRhSi is very likely also connected with large changes in the FS, which have to be taken into account in the controversial analysis and discussion of anomalies observed at the quantum critical point in this system.
Siの反強磁性転移の観測藤森 伸一; 山上 浩志; Gttler, M.*; Vyalikh, D. V.*; Laubschat, C.*; Seiro, C.*; Geibel, C.*
no journal, ,
The electronic structure of EuRhSi was studied by angle resolved photoelectron spectroscopy (ARPES) with soft X-ray (
eV). EuRhSi is a divalent Eu-based compound which exhibits an antiferromagnetic transition at 
K. The spectra consist of Eu 4f multiplet structure in the energy region of 
eV, and dispersive bands originated from ligand states. The Eu 4f multiplets exhibit energy dispersions, suggesting they have a hybridization with the ligand states. Temperature dependence of ARPES spectra was clearly observed in the Eu 4f multiplet structure particularly around the 
point, which is caused by the folding of the Brillouin zone due to the antiferromagnetic transition. We discuss the nature of the antifferomagnetic transition in EuRhSi in terms of its band structure and Fermi surface.
