Diploma - Max Planck Institute for Solid State Research

2 1 Introduction
conflicting limits of itinerant and localized electrons, a feasible, general solution is still
missing and therefore the dominating energy scales for each material’s type determine
the applicable approximations. Since photoelectron spectroscopy represents a surface
sensitive technique, surface preparation is a very delicate question. The present thesis
deals with ternary silicides of the type RE Rh 2 Si 2 which are available in form of rather
large single crystalls, that reveal a layered structure and may, thus, easily be cleaved
under ulta-high vacuum conditions leading to clean and structurally ordered surfaces.
While YbRh 2 Si 2 is a well-known heavy-fermion system which is close to a quantum
critical point and has been studied extensively in the recent past [7–9], EuRh 2 Si 2 is
a stable divalent antiferromagnet with almost unknown properties. The intention of
this diploma thesis is to present a detailed analysis of PE results of EuRh 2 Si 2 considering
both, surface and bulk, contributions which is mandatory because of the surface
sensitivity [10]. In addition, the interplay between the 4f electrons and the itinerant
conduction electrons is explored with the attempt of disentangling ground state’s from
excited state’s properties. A similar analysis has been prepared for YbRh 2 Si 2 indicating
that the former are at least to some extent accessible by photoemission [11]. In order
to study the interaction of the two electron species, the PE spectra are simulated using
ab initio density functional theory (DFT) calculations and a simple hybridization model
whereat the main challenge is the accurate treatment of the localized 4f electrons within
these methods.
The present thesis is organized as follows: at first, the key concepts of DFT and the
primarily-used methods are presented followed by a sketch of the PE process and a
description of the utilized experimental stations with their special properties. Subsequently,
EuRh 2 Si 2 is briefly introduced including an overview of the crystal structure,
the band structure, possible cleavage planes and different computational setups. The
analysis for different surface configurations and a disentanglement of surface and bulk
contributions followed by a detailed discussion of the coupling as well as the simulation
of the PE spectra is presented afterwards. Finally, an outlook regarding peculiar surface
states and a summary are given.