Unexpected differences between surface and bulk spectroscopic and implied Kondo properties of heavy fermion CeRh2Si2

Abstract

Ultra-violet angle-resolved photoemission spectroscopy (UV-ARPES) was used to explore the temperature dependence of the Ce-4f spectral responses for surface and bulk in the antiferromagnetic Kondo lattice CeRh2Si2. Spectra were taken from Ce- and Si-terminated surfaces in a wide temperature range, and reveal characteristic 4f patterns for weakly (surface) and strongly (bulk) hybridized Ce, respectively. The temperature dependence of the Fermi level peak differs strongly for both cases implying that the effective Kondo temperature at the surface and bulk can be rather distinct. The greatly reduced crystal–electric-field (CEF) splitting at the surface gives reason to believe that the surface may exhibit a larger effective Kondo temperature because of a higher local-moment effective degeneracy. Further, the hybridization processes could strongly affect the 4f peak intensity at the Fermi level. We derived the k-resolved dispersion of the Kondo peak which is also found to be distinct due to different sets of itinerant bands to which the 4f states of surface and bulk Ce are coupled. Overall our study brings into reach the ultimate goal of quantitatively testing many-body theories that link spectroscopy and transport properties, for both the bulk and the surface, separately. It also allows for a direct insight into the broader problem of Kondo lattices with two different local-moment sublattices, providing some understanding of why the cross-talking between the two Kondo effects is weak.

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

“…Our observations imply that this material exhibits novel temperature scales near the surfaces that can be in remarkable difference to those in the bulk. 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.…”

“…[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).…”

“…This targeted engineering makes it possible to directly and precisely study the diversity of 4f-driven physics at surfaces and interfaces. [6,9,10,13] The latter is essential for the elaboration of novel structural units which can be further used for the development of nanostructural materials for diverse applications. [22] However, such detailed fundamental studies are still missing for a wide range of remarkable crystal-structure families like the aforementioned Ce "115" materials which include CeCoIn 5 , CeRhIn 5 , and CeIrIn 5 .…”

The first-principles research on the role of surface in the heavy fermion compound CeRh$_2$Si$_2$

“…More importantly, the layered structure of CeRh 2 Si 2 single crystal can be technically cleaved with different terminated atoms [18][19][20][21] . Recently, different electronic structures of Si-and Ce-terminated CeRh 2 Si 2 were reported by high-precision ARPES and temperature dependent UV-APRES 11,22 . In these experimental results, the strength of Kondo resonance peak, Kondo temperature and other fine structure around Fermi level show notable differences between the samples with Si-and Ce-terminated surfaces, which indicates the hybridization strength and crystal electric field are affected by the different surface environments.…”