SPring-8, the large synchrotron radiation facility

Speaker : Dr. Denis Vyalikh

Language : English

Affiliation : Institute of Solid State Physics, University of Technology Dresden, Germany

Title : Photoemission studies of fine electronic structure and magnetism in RERh₂Si₂ (RE = Yb, Ce, Eu & Gd) systems

Abstract:
　For a long time, rare-earth (RE) intermetallic materials have attracted considerable interest because of their exotic properties at low temperatures which include complex magnetic phases, valence fluctuations, heavy-fermion states, Kondo behavior and many others. It is widely believed that all of these properties stem from the delicate interplay between almost localized 4f electrons and itinerant valence band states.
　Our experiments aim to disclose details of this interaction, and reveal the fine electronic structure of such materials near the Fermi level. To this end, we apply Angle-Resolved Photoemission Spectroscopy (ARPES) technique, which in spite of its surface sensitivity when working in UV mode, indeed, allows to gain deep insight not only into surface electron structure, but to probe the bulk derived states, too. In that regard, the particular point of our experiments is the proper discrimination of (sub-) surface and bulk related phenomena.
　In the past years we performed extensive ARPES studies on the RERh₂Si₂ (RE = Yb, Ce, Eu and Gd) series of compound as well as on YbIr₂Si₂ With our approach we were able to address some of the topics at the core of strongly correlated 4f electron systems: (i) observation of crystal-electric field (CEF) splitting of the 4f states and their fine dispersion induced by f-d hybridization; (ii) insight into the Fermi surface and manifestation of its strong 4f character. Disclosing its topology and features reflecting f-d coupling at the surface and bulk of the material. Studying its temperature dependence for a Kondo lattice (YbRh₂Si₂); (iii) clear evidence of the interplay of Dirac fermions and heavy quasi-particles; (iv) manifestation of unusual and strong ferromagnetism at the Si-terminated surface of an antiferromagnets (comparison between EuRh₂Si₂ and GdRh₂Si₂) caused by buried 4f magnetic moments; its relation to bulk AFM transition.

[1]K. Kummer, et al., Temperature invariant Fermi surface in the Kondo lattice YbRh₂Si₂, Phys. Rev. X 5 011028 (2015).
[2]M. Güttler, Tracing the localization of 4f electrons: ARPES on YbCo₂Si₂, the stable trivalent counterpart of the heavy-fermion YbRh₂Si₂, Phys. Rev. B 90 195138 (2014).
[3] A. Chikina et. al., Strong ferromagnetism at the surface of an antiferromagnet caused by buried magnetic moments, Nature Communications 5, 3171 (2014).
[4]. S. Patil et al., Crystalline Electric Field Splitting of 4f States in YbIr₂Si₂: An ARPES View JPS Conf. Proc. 3 011001 (2014).
[5] M. Höppner et. al., Interplay of Dirac fermions and heavy quasiparticles in solids, Nature Communications 4, 1646 (2013)
[6] S. Danzenbächer et. al., Insight into the f-derived Fermi surface of the heavy-fermion compound YbRh₂Si₂, Phys. Rev. Lett. 107, 267601 (2011).
[7] D.V. Vyalikh et. al., k-dependence of the crystal-field splittings of 4f states in rare-earth systems, Phys. Rev. Lett. 105, 237601 (2010).

Organizer : Fujimori Shin-ichi
Mail : fujimori@spring8.or.jp
PHS : 3914