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Abstract:
YbCo2Si2 is considered to serve as a stable-valent, isoelectronic
reference for the extensively studied heavy-fermion system YbRh2Si2
which is situated very close to an antiferromagnetic quantum critical
point (QCP). The investigation of the Fermi surface (FS) topology of
YbCo2Si2 and its comparison to YbRh2Si2 could help to unravel the
strongly disputed nature of this quantum phase transition, whether it
originates from a "local" or "itinerant" QCP. Here we study the
electronic structure and FS of YbCo2Si2 by means of angle-resolved
photoelectron spectroscopy (ARPES) and compare it to ab initio band
structure calculations and FS modeling. Our approach allows the
electronic structure at the surface and in the bulk to be disentangled.
Identifying the bulk contribution, we demonstrate that YbCo2Si2 exhibits
a "small" FS, confirming the formation of a "large" FS in YbRh2Si2. This
favors an itinerant QCP, instead of the widely discussed local scenario.
Our study demonstrates that ARPES is a reliable tool for the study of
bulk electronic states in intermetallic Kondo lattice systems despite
the complexity induced by their three-dimensional character and the
presence of pronounced surface states.
