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L. Reisinger:
"Studies of magnetic and electronic properties of quasi-one-dimensional metals";
Betreuer/in(nen): H. Michor; Institut für Festkörperphysik, 2021; Abschlussprüfung: 26.04.2021.

Dimensionality is an important aspect in solid state physics and frequently connected to emergent phenomena such as high-temperature superconductivity, dimensionally frustrated magnetism and various others. One of these is the Peierls charge density wave instability which occurs in crystals with a quasi-one-dimensional electronic structure. This can result from crystal structures with chain-like building blocks but also appears under specific bonding conditions in typical three-dimensional crystals. The charge density wave transition (CDW) causes a modulation of the lattice which enlarges the periodicity in real space and therefore results in an inverse alteration of the Brillouin zone size, giving rise to extraordinary features like non-linear transport which may find use in modern electronic applications.
The motivation of this master thesis is divided into three aspects revolving around the electronically quasi-one-dimensional rare-earth nickel dicarbides (RNiC₂). Supplementary to single crystal diffraction experiments carried out by specialists, the nature of the structural and electronic modifications at phase transitions were examined with dilatometry, heat capacity and resistivity measurements. Characteristic features of the first and second order CDW transitions were distinguished. By applying the Clausius-Clapeyron and a modified Ehrenfest relation, it is revealed that the commensurate CDW order parameter is stabilized by pressure while the incommensurate order parameter is rather destabilized by pressure. Additionally, the magnetic ground state of PrNiC2 was analyzed in order to ascertain possible dynamic frustration. The crystal field parameters and the energy level splitting due to the impact of the crystalline electric field were evaluated for PrNiC₂. Moreover, pseudo-ternary solid solutions of LuNi_1-xCo_xC₂ were grown in the optical floating zone furnace in order to determine the CDW critical point in dependence of the Ni/Co composition. It has earlier been attempted to discover the suppression of the CDW in polycrystalline samples which however due to emerging compositional inhomogeneity has been feasible only for very small degrees of substitution and accordingly small reductions of the Peierls temperature. Using the floating zone melting technique, it was possible to grow more homogeneous solid solutions, whereby the critical point of the suppression of the CDW state could be located to LuNi_(0.85-0.8)Co_(0.15-0.2)C₂.

http://dx.doi.org/10.34726/hss.2021.76492