Chimie Douce Approaches to Quantum Materials Synthesis

Over the past few decades, the forefront of materials physics has undergone a quiet revolution, ushering in the age of topological quantum materials. Earlier concepts holding that changes in a material's ground state were always intimately related to changes in symmetry have been expanded. It is now understood that there are "topological systems" where the state can be altered even though the symmetry remains unchanged. Among these systems, quantum spin liquids (QSLs) are of particular interest as paradigmatic examples which can be described in simple terms theoretically but exhibit strongly entangled quantum ground states and non-trivial topology. The hallmark of the QSL is the fractionalization of collective magnetic excitations that correspond to exotic particles such as Anyons or Majorana Fermions rather than the simple bosons (magnons) existing in conventional ordered magnets.

The research presented in this dissertation addresses the urgent need to find physical realizations of QSLs. In 2006 theorist A. Kitaev invented an exactly solvable model of a QSL based on a honeycomb lattice of S=1/2 spins connected by mutually incompatible Ising interactions[1]. In 2009, Jackeli and Khaliullin (JK) published a seminal paper that proposed a pathway to realize a Kitaev quantum spin liquid in a real material [2].

In the research presented here, we emphasize using chimie douce or "soft chemistry" approaches to the synthesis of new quantum materials, including intercalation, ion exchange, and hydrothermal techniques. Although these techniques are not new, it is only in the past few years that they have begun to have an appreciable impact on materials physics. The reason soft chemistry approaches are gaining ground is that they offer an incredible synthetic richness compared to traditional thermodynamic approaches.

In this dissertation, we study some new honeycomb delafossite systems, Ag₃LiM₂O₆ (M = Ru⁴⁺, Rh⁴⁺, Ir⁴⁺), in which the materials are synthesized using a gentle ion-exchange technique. We also study graphite that has been intercalated with RuCl₃. RuCl₃ is known to be "proximate" to a Kitaev QSL, and we hypothesized that by intercalating RuCl₃ into graphite, we could push RuCl₃ closer to an ideal Kitaev QSL.