Diploma - Max Planck Institute for Solid State Research

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5 Summary
In this diploma thesis angle-resolved photoemission spectroscopy and density functional
theory based calculations have been used to study the ternary rare-earth compound
EuRh 2 Si 2 . Thereby the emphasis was laid on many-body interactions exploring the
interplay of two opposing limits for the description of electrons: itinerant character vs.
localization. Symmetry dependencies of photoemission as depicted in fig. 5.1 have been
neglected.
The crystal cleaves solely along the Eu–Si planes which has been demonstrated theoretically
by force-minimization. The amount of europium atoms at the surface of the
sample is not controllable, therefore one has to search for regions at the surface which
are predominantly terminated by Si or Eu atoms. The kind of termination may be
identified by the surface component of the Eu 4f emission which is shifted by approximately
1 eV to higher binding energies whereat it is missing for Si termination. On
the other hand, a star-like surface state centered around the M-point of the quadratic
surface BZ located in a gap of the projected Fermi surface manifests Si termination in
agreement with results of slab calculations. For the first time, a linear dispersive Diraclike
state around the Γ-point has been observed for a rare earth compound. It seems
to be of surface origin and has its nodal point close above (below) the Fermi energy at
Si (Eu) terminated surfaces. This observation is in accordance with the surface calculations
(4f treated as core orbitals) indicating that the pertubation of the eigenvalues due
Figure 5.1: PE spectra
of EuRh 2 Si 2 with
Si termination for different
polarisations
at hν = 100 eV and
T ≈ 2 K, aligned roughly
in X − Γ − X direction
(1 3 ARPES (BESSYII))
(a) has been measured
with horizontal polarisation
and (b) with linear
vertical polarisation. In
comparison to SLS-SIS
the polarization effect
seems to be swapped
(cf. fig. 4.8a)