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Low temperature properties of strong spin-orbit systems

  • Author(s): Trinh, Jennifer
  • Advisor(s): Ramirez, Arthur P
  • et al.
Abstract

Spin-orbit coupling (SOC) is a relativistic interaction between the electronic spin and orbital degrees of freedom. The SOC can give rise to a variety of interesting phenomena, most notably at low temperatures in compounds composed of large-Z (atomic number) elements, since the SOC scales as Z^4. In this dissertation, I examine the low-temperature expression of SOC in the transport and magnetic properties of a representative selection of materials, including the heavy fermion system URu2Si2, narrow band gap semiconductor FeSb2, 5d transition metal oxide BaIrO3, linear band CoSb3 and RhSb3 skutterudites, as well as a new class of rare earth materials on a novel kagome lattice with non-collinear Ising axes, called the “tripod” kagome lattice. These compounds all feature unusual many-body properties that are either directly or indirectly linked to the large SOC present in each. In URu2Si2, for example, the large SOC is foundational to the hidden order (HO) phase that arises at T_HO = 17.5 K, where a remarkable magnetic signature is seen not in the linear magnetic susceptibility, χ_1, but in the leading nonlinear term χ_3. Exotic magnetic ground states are also seen in the newly synthesized rare earth tripod kagome systems. The SOC is also an important component of the inverted band structure in Dirac materials, and thus plays a role in the band formation of CoSb3 and RhSb3, which have both been predicted to be near a topological transition. Finally, large SOC may also be related to interesting carrier dynamics in FeSb2 and BaIrO3: FeSb2 displays a unique proportionality between the thermopower, S(T), and Hall mobility, μ_H (T), while BaIrO3 exhibits a non-saturating positive linear magnetoresistance, despite ferromagnetic order, which usually results in a negative saturating magnetoresistance. These examples showcase the importance of SOC across a range of strongly correlated phenomena spanning itinerant to localized electronic degrees of freedom.

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