First-principles study of bulk stacking, $J_{\mathrm{eff}}$ picture, magnetic Hamiltonian, $g$ factors, and structural distortions of $\alpha$-RuCl${}_3$

Abstract

$\alpha$-RuCl${}_3$ is a candidate Kitaev material that exhibits zigzag antiferromagnetic ordering below 7 K. One contentious issue regarding this material is its bulk structure in the low-temperature phase. Recently, it has become generally accepted from experiments that the low- and high-temperature structures belong to the $R\bar{3}$ and $C2/m$ space groups, respectively. However, there was no theoretical study supporting the $R\bar{3}$-type structure as the low-temperature structure. In this study, we use constrained density functional theory to show that the $R\bar{3}$ structure is lower in energy than the $C2/m$ structure, in agreement with experimental observations. Then, we show that the conduction band minimum states are almost of the $J_{\text{eff}}=1/2$ and $m_{\text{eff}}=-1/2$ character, if we set the angular momentum quantization axis to be parallel to the Néel vector; this is the first analysis of the $J_{\text{eff}}$ picture for $\alpha$-RuCl${}_3$ from this perspective. In addition, we compute the anisotropic magnetic exchange parameters and $g$ factors of monolayer $\alpha$-RuCl${}_3$, thereby providing a comprehensive understanding of its magnetism. Our results demonstrate that both second-nearest-neighbor exchange interactions and magnetic moments not captured by the conventional atomic orbital projection method are necessary for accurate description of the magnetism in $\alpha$-RuCl${}_3$. Moreover, the calculated $g$ factors are in fairly good agreement with experimental measurements, especially the small anisotropy between their in-plane and out-of-plane components. Finally, we examine the effects of structural distortions from a perfect RuCl${}_6$ octahedron, already present in bulk $\alpha$-RuCl${}_3$ without any external perturbation, on the magnetic properties. (The abstract is cut here due to the word limit; see the pdf file for the full abstract.)

References in corpus (13)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Mott Insulators in the Strong Spin-Orbit Coupling Limit: From Heisenberg to a Quantum Compass and Kitaev Models
• Novel Jeff = 1/2 Mott State Induced by Relativistic Spin-Orbit Coupling in Sr2IrO4
• Ising-Type Magnetic Ordering in Atomically Thin FePS3
• Successive magnetic phase transitions in $\mathbf{\alpha }$-RuCl${}_3$: XY-like frustrated magnet on the honeycomb lattice
• Kitaev magnetism in honeycomb RuCl3 with intermediate spin-orbit coupling
• Spin-wave excitations evidencing the Kitaev interaction in single crystalline $\alpha$-RuCl${}_3$
• Anisotropic Ru3+ 4d5 magnetism in the alpha-RuCl3 honeycomb system: susceptibility, specific heat and Zero field NMR
• High-pressure magnetization and NMR studies on $\alpha$-RuCl${}_3$
• Electronic and phonon excitations in α-RuCl${}_3$
• Contrasting electronic states of RuI3 and RuCl3
• Magnetothermal transport in ultraclean single crystals of Kitaev magnet $\alpha$-RuCl${}_3$