Electronic Phases in Crystalline Lanthanide Systems

Abstract

Crystalline lanthanide systems are known to realize a multitude of disparate electronic phases arising from lattices of localized f-electrons in the crystal. These phases include magnetic phenomena such as ferromagnetism and antiferromagnetism as well as nonmagnetic Fermi liquid phases such as heavy fermion systems. Lanthanide systems can moreover realize exotic phases such as heavy fermion superconductivity, multipolar order, and hidden order. The latter two may be driven not solely by the magnetic dipole moment of the localized f-electrons, but additionally by higher-order multipolar moments such as the electric quadrupole which are often significant due to the highly anisotropic nature of the f-electron orbital wavefunction. The orbital wavefunction is also highly sensitive to the local crystal field surrounding it via interaction with the crystal electric field (CEF). This crystal field can lower the symmetry of the environment wherein the f-electron lives to strongly modify the behavior of the free-space electronic state by lifting energetic degeneracies and introducing strong anisotropy.

This thesis will investigate the physics of three different lanthanide systems: R₃Ni₃₀B₁₀ (R = La, Ce), Ce₂SnS₅, and Gd₂B₅. These materials will provide opportunities to discuss multipolar/anomalous order in Ce₃Ni₃₀B₁₀, anisotropic magnetism in Ce2SnS5, and the mapping of a rich, highly anisotropic phase diagram in Gd₂B₅. Experimental characterization techniques employed in the study of these materials include electrical transport, SQUID magnetometry, torque magnetometry, and heat capacity. This thesis will also leverage group theory and its power to shed light on otherwise abstruse electronic phenomena. Due to the wide range of electronic phenomena accessible through the study of lanthanide systems, these materials provide an exciting platform for the realization of material engineering of potentially tunable quantum systems. This thesis will motivate these systems by emphasizing the richness of the myriad of electronic phenomena attainable through the manipulation of the local environment of the lanthanide f-electrons.