Photoelectron diffraction for probing valency and magnetism of 4f -based materials: A view on valence-fluctuating EuIr2Si2

Abstract

We present and discuss the methodology for modeling 4 f photoemission spectra, 4 f photoelectron diffraction (PED) patterns, and magnetic dichroism effects for rare-earth-based materials. Using PED and magnetic dichroism in photoemission, we explore the electronic and magnetic properties of the near-surface region of the valence-fluctuating material EuIr 2 Si 2. 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 fifth 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 (fourth atomic layer below the surface) behaves divalently and orders ferromagnetically below 48 K. 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 (eighth 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 presented approach and obtained results create a background for further studies of exotic surface properties of 4 f-based materials, and allow us to derive information related to valency and magnetism of individual rare-earth layers in a rather extended area near the surface.

Strong Rashba Effect and Different f−d Hybridization Phenomena at the Surface of the Heavy‐Fermion Superconductor CeIrIn5

“…This is in line with the recently reported unusual T dependencies for surface and bulk with evaluation of the corresponding Kondo-related temperatures for heavy-fermion antiferromagnet CeRh 2 Si 2 [10,36] as well as with observation of emergence of 2D ferromagnetism and Rashba spin-orbit coupling at iridium-silicide surface of valence-fluctuating EuIr 2 Si 2 . [6,7] Thus, our findings suggest that CeIrIn 5 becomes appealing for temperature-dependent studies of the surface-related properties and namely how its exotic f-driven physics is modified upon approaching the surface region where Rashba SOCrelated phenomena emerge. Our results call for detailed studies of the properties emerging at the surfaces of many strongly correlated Ce, Eu, and Yb materials with layered, quasi-2D structure.…”

“…[1][2][3][4][5] Recent photoemission insights into the electronic and magnetic properties of silicide-and rare-earth-terminated surfaces of strongly correlated electron materials of the RET 2 Si 2 family (RE and T are rare-earth and transition-metal atoms, correspondingly) have unveiled novel temperature scales linked with the Kondo interaction, heavy-fermion behavior, mixed-valent properties, and exchange magnetism that are remarkably different to those in the bulk. [6][7][8][9][10][11][12][13][14] Essentially, these studies illustrate that the surfaces of strongly correlated materials with a quasi-2D structure can be viewed as versatile platforms for unveiling novel f-driven phenomena and disentangling the different surface and bulk contributions to the aforementioned many-body effects. This calls for consideration of other classes of strongly correlated materials possessing layered atomic structures like, for example, the CeTIn 5 (T = Co, Rh, Ir) family.…”

“…[18,19] The aforementioned RET 2 Si 2 materials, which crystallize in the layered, body-centered tetragonal ThCr 2 Si 2 structure, exhibit a rich diversity of f-driven properties. In order to unravel the surface-related phenomena and respective temperature scales, comprehensive experimental and theoretical studies were performed for the mixed-valent material EuIr 2 Si 2 , [6][7][8] the heavyfermion compounds YbRh 2 Si 2 , [20,21] YbIr 2 Si 2 , [9] and CeRh 2 Si 2 [10] as well as for the antiferromagnets GdIr 2 Si 2 , [11] TbRh 2 Si 2 , [12] GdRh 2 Si 2 , [13] and HoRh 2 Si 2 . [14] Due to their quasi-2D structure, the respective samples can be easily cleaved and examined with surface-sensitive ultra-violet angle-resolved photoelectron spectroscopy (UV-ARPES).…”