Kitaev Quantum Spin Liquids

TL;DR

Kitaev quantum spin liquids are exotic states with fractionalized excitations and topological order, offering insights into quantum entanglement and potential for quantum computing, with ongoing research into candidate materials like RuCl3.

Contribution

This review synthesizes current research on Kitaev QSLs, emphasizing candidate materials and experimental evidence, and highlights future research directions.

Findings

Evidence of spin fractionalization in RuCl3

Kitaev model's connection to topological quantum computation

Transition to chiral spin liquid under magnetic field

Abstract

Quantum spin liquids (QSLs) represent exotic states of matter where quantum spins interact strongly yet evade long-range magnetic order down to absolute zero. Characterized by non-local quantum entanglement and resultant fractionalized excitations, QSLs have emerged as a frontier in condensed matter physics, bolstered by the recent identification of several candidate materials. This field holds profound implications for understanding strong correlations, topological order, and emergent phenomena in quantum materials. Among them, the Kitaev model, featuring bond-directional Ising interactions, provides a rare exactly solvable QSL example. Its ground state is a topological QSL, with spin degrees of freedom fractionalized into emergent Majorana fermions. Under an applied magnetic field, the Kitaev QSL transitions to a topologically non-trivial chiral spin liquid state with non-Abelian anyons, offering potential resources for topological quantum computation. The non-Abelian character of these anyons in the Kitaev QSL demonstrates a profound connection to certain topological superconductors and even-denominator fractional quantum Hall states. Since the theoretical prediction that the Kitaev model could manifest in spin-orbit-coupled materials such as honeycomb iridates and ruthenates, research has focused on identifying candidate compounds. In particular, experimental evidence suggests spin fractionalization and topological phenomena akin to the Kitaev model in the spin-orbit Mott insulator RuCl3. However, results and interpretations remain actively debated. This review begins with a brief review on QSLs in other systems, followed by a comprehensive survey of existing studies on Kitaev candidate materials, with a particular focus on RuCl3. Rather than offering conclusive remarks, our aim is to inspire future research by examining several key aspects of the current literature and perspectives.