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

Georg Poelchen,Cornelius Krellner,Nubia Caroca-Canales,Steffen Danzenbächer,Alexander V Fedorov,Clemens Laubschat,Dmitry Yu Usachov,Yuri Kucherenko,Victor N Antonov,James W Allen,Denis V Vyalikh,Christoph Geibel,Monika Güttler,Max Mende,Kurt Kummer,Alexander Generalov,Pavel Dudin,Kristin Kliemt,Susanne Schulz

doi:10.1038/s41535-020-00273-7

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.

Highlights

Rare-earth (RE) intermetallics with an unstable valence form a prototype of strongly correlated electron systems, where the correlations arise from the interplay between almost localized 4f electrons and itinerant valence-band states
The crystal electric field (CEF) is characterized by weak components “in plane” due to the charged Ce-neighbor atoms and a strong component perpendicular caused by the interval are shown in the lower panels
We have presented the results of T-dependent vacuum ultra-violet (VUV)-angle-resolved photoemission spectroscopy (ARPES) measurements on the AFM Kondo lattice CeRh2Si2

Summary

Introduction

Rare-earth (RE) intermetallics with an unstable valence form a prototype of strongly correlated electron systems, where the correlations arise from the interplay between almost localized 4f electrons and itinerant valence-band (spd) states They lead to a wealth of extraordinary phenomena like the formation of ultraheavy quasiparticles (heavy fermions), unconventional superconductivity, magnetic order, and non-Fermi liquid ground states, that may even be degenerate with each other at quantum critical points of their phase diagrams[1,2,3,4,5,6]. The Ce-4f emissions reveal a characteristic structure with a feature at a binding energy (BE) of about 2 eV corresponding roughly to a Ce-4f 0 final state and a spin–orbit (SO) split structure at the Fermi energy (EF) exhibiting mainly 4f1 character The appearance of the latter is a hybridization effect making this feature sensitive to the valence-band structure and crystal electric field (CEF). The 4f1 emission attracts particular interest, consisting of a narrow peak at EF, which is attributed to the tail of the Kondo resonance lying slightly above EF7, and its satellites[7,8,9,10,11]

Methods

Results

Conclusion