Ground States And Behaviors In Correlated Electron Materials
Author | : Alex M. Konic |
Publisher | : |
Total Pages | : 0 |
Release | : 2023 |
ISBN-10 | : OCLC:1409166266 |
ISBN-13 | : |
Rating | : 4/5 (66 Downloads) |
Book excerpt: Heavy Fermion materials are a class of correlated electron materials that are best known for their partially filled 4-f and 5-f electron orbitals. These partially filled electron orbitals cause the formation of local magnetic moments within many of these materials which can lead to a vast array of interesting interaction with the conduction electrons. These interactions often manifest themselves as interesting physical phenomena, such as superconductivity, Fermi liquid/non-Fermi liquid behavior, magnetic ordering, and quantum criticality. In this work, we report on heat capacity measurements for a group of "1-2-20 cage compounds", and magnetoresistivity measurements for a samarium doped cerium based superconductor. Motivated to ascertain a better understanding of the electronic structure of these cage compounds, we first investigated multiple praseodymium and cerium based 1-2-20 cage compounds through heat capacity measurements down to 0.4 K and in magnetic fields up to 14 T. This analysis illuminated the ground state of the PrNi2Cd20 and PrPd2Cd20 materials to be non-Kramers doublet states, while for CeNi2Cd20 and CePd2Cd20, the ground state was a Kramers doublet. Further investigation into the cerium based compounds indicated that the lack of magnetic order normally seen in cerium based heavy fermions could potentially be attributed to this ground state driving a minimal Ruderman-Kasuya-Kittel-Yosida (RKKY) interaction strength in the material. We also analyzed samarium doped CeCoIn5, motivated to further explore the quantum critical behavior of this material and how it interacts with magnetism. Resistivity measurements in Ce1-xSmxCoIn5 display a clear onset of the Kondo effect within the material, evidenced by a local resistivity minimum. A closer inspection of the resistivity in this material shows that it can be expressed as a superposition of two portions, one positive and one negative. By separating the resistivity in this way, we can more closely examine the different physics at play, and how changes, such as doping concentration, effect the physical phenomena that occur. This analysis indicates that as the samarium concentration is increased, the material moves closer to the single impurity limit as Kondo coherence effects are lessened. Additionally, it can be seen through magnetoresistivity that this material exhibits two Kondo regimes, one conventional and one unconventional. We show that in the unconventional regime, the magnetic field required to break coherence effects increases, rather than decreases, potentially due to field quenching effects on spin fluctuations. Lastly, we examine the behavior of the field induced quantum critical point and its behavior as the samarium concentration changes. We found that as the samarium concentration increases, the field induced quantum critical point is rapidly suppressed, until it vanishes at a certain concentration. The same behavior can also be seen in the superconducting critical temperature, indicating that superconducting in this material could be mediated by anti-ferromagnetic (AFM) spin fluctuations.