Author ORCID Identifier

https://orcid.org/0000-0002-1349-4965

Date Available

7-20-2025

Year of Publication

2025

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Arts and Sciences

Department/School/Program

Physics and Astronomy

Faculty

Dr. William J. Gannon

Faculty

Dr. Anatoly Dymarsky

Abstract

We present studies of three independent solid state materials: CeGaGe, CsSnI3, and Yb2Si2-xGexAl.

CeGaGe is a magnetic candidate Weyl semimetal. Magnetic Weyl semimetals have possible technological applications due to their electronically conducting bulk states, magnetic states, and topologically protected surface states. We grew single crystals of CeGaGe using the zone-refinement method and flux-growth method. With single crystal X-ray and neutron diffraction, we found that zone-refined CeGaGe crystallizes with the I41md symmetry (space group 109). With single crystal X-ray diffraction, we found that flux-grown samples of CeGaGe have the I41md symmetry at room temperature, but undergo a structural transition somewhere between room temperature and 100 K to the P41 symmetry (space group 76) and/or the P43 symmetry (space group 78). P41 and P43 are enantiomers and only differ by their chirality. This structural transition is not known to happen in other Weyl semimetals with similar composition and room-temperature structure. We found the magnetic structure of flux-grown CeGaGe with powder neutron diffraction. The magnetic structure of flux-grown CeGaGe with the P43 crystal symmetry is chiral and incommensurate along the crystal c-axis.

CsSnI3 is an inorganic halide perovskite. Inorganic halide perovskites have applications in solar energy harvesting and light emission. Quantum coherent transport has also been observed in halide perovskites. A recent study of single-domain, epitaxial thin films of CsSnI3 found extraordinarily long quantum phase coherence length, indicating that CsSnI3 is a good material for investigating coherent quantum electronic effects because the extended coherence length allows for quantum interference effects to be observed over a larger scale than seen in most materials. We present a study on granular CsSnI3 thin films that was conducted to probe the effects of grain size on quantum coherence length. It was found that all granular thin film samples had coherence lengths an order of magnitude lower than epitaxial thin films. However, the particular grain size of different granular thin films showed little effect on the coherence length. It is proposed that the higher symmetry of the tetragonal epitaxial thin films causes higher coherence lengths than in the lower symmetry orthorhombic granular thin films due to the higher phonon density of states in the orthorhombic granular thin films leading to increased electron-phonon scattering.

Yb2Si2-xGexAl is a doped heavy-fermion compound that features 2-dimensional Shastry-Sutherland Lattice (SSL) planes of magnetic Yb ions. Shastry-Sutherland compounds are promising for study of quantum correlations on a frustrated lattice and have the possibility to exhibit quantum phase transitions as the lattice may be distorted to favor either the dimer fluid phase or the antiferromagnetic phase. The SSL of Yb2Si2Al favors the dimer fluid phase and therefore we attempted to study a quantum phase transition by distorting the lattice to favor the antiferromagnetic phase via substituting Ge for Si using varying molar concentrations of Ge. No quantum phase transition was induced with any molar concentration of Ge doping, but various physical properties changed with varying concentrations of Ge doping. We report structural, physical, and magnetic properties of Yb2Si2-xGexAl which we measured with standard Bruker X-ray diffractometers, a standard Quantum Designs Physical Property Measurement System, and a standard Quantum Designs Magnetic Property Measurement System respectively. All samples have Sommerfeld coefficient γ greater than 60.7(6) mJ/K2 mol Yb, indicating that the samples are heavy-fermion compounds. All samples have Wilson ratios near 1/2, which is consistent with other heavy fermion compounds.

In each of the material presented in this study, the physical properties are intimately linked with the material structure.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2025.295

Funding Information

The D8 Venture diffractometer used in studies presented in this dissertation was funded by the National Science Foundation Major Research Instrumentation Award (NSF-CHE-1625732) and by the University of Kentucky.

Download

Share

COinS