Tracing the localization of4felectrons: Angle-resolved photoemission onYbCo2Si2, the stable trivalent counterpart of the heavy-fermionYbRh2Si2

Abstract

${\mathrm{YbCo}}_{2}{\mathrm{Si}}_{2}$ is considered to serve as a stable-valent, isoelectronic reference for the extensively studied heavy-fermion system ${\mathrm{YbRh}}_{2}{\mathrm{Si}}_{2}$ which is situated very close to an antiferromagnetic quantum critical point (QCP). The investigation of the Fermi surface (FS) topology of ${\mathrm{YbCo}}_{2}{\mathrm{Si}}_{2}$ and its comparison to ${\mathrm{YbRh}}_{2}{\mathrm{Si}}_{2}$ 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 ${\mathrm{YbCo}}_{2}{\mathrm{Si}}_{2}$ 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 ${\mathrm{YbCo}}_{2}{\mathrm{Si}}_{2}$ exhibits a ``small'' FS, confirming the formation of a ``large'' FS in ${\mathrm{YbRh}}_{2}{\mathrm{Si}}_{2}$. 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.