Electronic States of Heavy Fermion Materials

The de Haas-van Alphen (dHvA) effect is one of the most powerful and straightforward methods of determining the electronic structure of metals, knowledge of which is essential to understanding the observed physical properties such as resistivity, magnetic structure, and specific heat. Of interest in the field of condensed matter physics are the so-called heavy fermion materials: compounds involving rare earth metals in which strong correlation effects cause the electrons to behave as if they are orders of magnitude heavier than a bare electron. To enable measurement of these materials, I maintained our in-house data collection system known as DAVIES. Long standing issues in network communication between the involved computers have been mitigated or solved, improving the overall ease of measurement. Using DAVIES and our 3He/4He dilution refrigerator, I completed field modulation dHvA measurements on samples of YbRh2Si2 for field sweeps of 16-13 T and sample rotations from (100)-(110), (100)-(001), and (110)-(001). This yielded the first observation of an orbit that could be attributed to the J-sheet of the Fermi surface. The rotation measurements were compared against basic band structure calculations, which I completed, and more advanced band structure calculations. The calculations are in good agreement with the experimental results, though the ad hoc fitting method requires a more thorough examination to better understand the origin of this agreement. I also conducted field modulation dHvA measurements on one sample of PrOs4Sb12 for sweeps of 10-7 and 6-3 T at temperatures from about 25-2800 mK. A novel technique, which examines the phase of the quantum oscillations, was utilized to explore the occupancy of the Pr crystal field levels and the lower antiferroquadruploar (AFQ) phase boundary. These results were compared against mean field calculations, which took into account nearest neighbor quadrupolar coupling and the hyperfine interaction in the Hamiltonian. We obtained good agreement of the theoretical and experimental phase boundary, except at the lowest temperatures, in which a tail was predicted by calculations but not observed by experiment. This lead to the conclusion that further refinement of our mean field theory would be an interesting pursuit for future research into this material.Ph.D