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Ultrafast Dynamics of Coupled Charge, Spin, and Orbital Degrees of Freedom in Perovskite-based Mott-Hubbard Insulators

  • Author(s): Lovinger, Dylan
  • Advisor(s): Averitt, Richard D
  • et al.
Abstract

The coupling of charge, spin, and orbital degrees of freedom gives rise to a wide range of emergent physics, resulting in numerous materials with interesting electronic and magnetic properties. Among these are Mott-Hubbard insulators, whose electronic interactions lead to a ground state that cannot be described by a non-interacting band theory. In this work we study two such materials, LaVO$_3$ (LVO) and GdTiO$_3$ (GTO), using ultrafast optical pump-probe reflectivity and magneto-optical Kerr spectroscopy. These time-resolved techniques allow us to partially disentangle the competing degrees of freedom, giving insight into how they interact at their fundamental timescales when driven out of equilibrium. By studying the excitation and relaxation dynamics we observe signatures of the spin and orbital order phase transitions, as well as evidence of how they couple to other degrees of freedom. In LVO this coupling gives rise to exciton formation, bound electron-hole pairs that arise from the interaction of with a spin and orbitally ordered lattice. In GTO, we observe correlation of an acoustic phonon to the magnetic order, indicative of magneto-elastic coupling. This involves transient strain-induced modification of the magnetic exchange interaction, resulting in a novel method of coupling light to the magnetic degrees of freedom. These effects highlight the physics that emerges from strongly coupled degrees of freedom, and our results provide new ways to understand and manipulate them.

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