Session 1-4

Abstract

Quantum spin liquid (QSL) represents a novel phase of matter, where interacting spins remain fluctuating down to zero temperature and form a quantum-mechanically entangled state. QSL has been a long-sought-after dream in condensed matter physics, and several candidate materials and theoretical models have been put forward. The Kitaev honeycomb model is one of the theoretical proposals, which is characterized by the bond-dependent Ising magnetic interactions on a honeycomb lattice [1]. Kitaev showed that the model is exactly solvable by introducing two types of Majorana fermions and the ground state is shown to be a QSL. Soon after this proposal, a microscopic theory predicted the appearance of Kitaev-type bond-dependent magnetic interactions in heavy transition-metal compounds forming spin-orbit-entangled J_eff = 1/2 states [2]. 5d honeycomb iridates and 4d RuCl₃ have emerged as a potential realization of Kitaev spin liquid [3]. In reality, most of those “Kitaev materials” display long-range magnetic order at low temperatures, which has been attributed to the presence of additional magnetic interactions other than Kitaev-type, including Heisenberg and off-diagonal interactions. The prime challenge in Kitaev materials is therefore to suppress the undesired magnetic interactions.

3d honeycomb cobaltates have appeared to be a new platform of Kitaev physics. The high-spin 3d7 configuration of Co2+ ion may form a spin-orbit-entangled J_eff = 1/2 state, yielding Kitaev-type coupling as in 5d5 iridates [4]. Notably, more localized character of 3d electrons, compared to 4d and 5d counterparts, is expected to suppress competing magnetic interactions. In this presentation, I will discuss materials challenges towards the realization of Kitaev QSL and our exploration for spin-orbit-entangled cobaltates which may realize Kitaev physics.