Kristin Kliemt, Institute of Physics, Goethe-University

(Note the date change!)

The study of collective phenomena raising from enhanced coupling between electrons and phonons is focused
on materials which exhibit phase transitions involving both, electronic and lattice-degrees of freedom. One system
providing such a strongly coupled phase transition is EuPd2Si2 of the ThCr2Si2 structural type. This compound
shows a temperature induced valence transition of europium between the energetically vicinal valence states Eu2+
and Eu3+ at about 170 K [1] which is connected to a strong change in the a lattice parameter. First reports on the
synthesis of single crystals came up only recently [2], but a deep investigation of the valence transition in this
compound is still missing, especially the location of the system in the generalized phase diagram is under
investigation. We aime to tune the system by negative chemical pressure towards a possible second order critical
endpoint in this phase diagram via substitution of Si by Ge.
We applied the Czochralski method using a levitating melt under enhanced Ar pressure for the successful
growth of mm-sized single crystals of EuPd2Si2. Recently, this procedure was developed and successfully applied
to the single crystal growth of the ferromagnetic quantum-critical compound YbNi4P2 [3]. In this talk, we will
present the characterization of EuPd2Si2 crystals as well as of the Ge substituted system and some preliminary
physical characterization around the valence transition. The combination of careful chemical and structural
analysis with magnetization and transport measurements shows that EuPd2Si2 grows in a homogeneity range and
that the physical properties are very sensitive to tiny changes in the composition of the sample.

[1] E. V. Sampathkumaran et al., Journal of Physics C14, L237 (1981).
[2] Y. Onuki et al., Philosophical Magazine 97, 3399 (2017).
[3] K. Kliemt, C. Krellner, J. Cryst. Growth 449, 129 (2016).