Abstract
Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago. A prominent case is the Kitaev spin liquid, host of remarkable properties such as protection of quantum information and the emergence of Majorana fermions. Here we discuss the promise for spin-liquid behavior in the 4d5 honeycomb halide α-RuCl3. From advanced electronic-structure calculations, we find that the Kitaev interaction is ferromagnetic, as in 5d5 iridium honeycomb oxides, and indeed defines the largest superexchange energy scale. A ferromagnetic Kitaev coupling is also supported by a detailed analysis of the field-dependent magnetization. Using exact diagonalization and density-matrix renormalization group techniques for extended Kitaev-Heisenberg spin Hamiltonians, we find indications for a transition from zigzag order to a gapped spin liquid when applying magnetic field. Our results offer a unified picture on recent magnetic and spectroscopic measurements on this material and open new perspectives on the prospect of realizing quantum spin liquids in d5 halides and oxides in general.
Highlights
Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago
Quantum spin liquids (SL’s) are states of matter that cannot be described by the broken symmetries associated with conventional magnetic ground states[1]
Our result is qualitatively consistent with the latter. Relevant in this regard is further the trends we observe for the effective K by running spin-orbit calculations at different levels of approximation: restricted open-shell Hartree-Fock (ROHF), complete-active-space self-consistent-field (CASSCF) and multireference configuration-interaction (MRCI)
Summary
Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago. A prominent case is the Kitaev spin liquid, host of remarkable properties such as protection of quantum information and the emergence of Majorana fermions. We discuss the promise for spin-liquid behavior in the 4d5 honeycomb halide α-RuCl3. Our results offer a unified picture on recent magnetic and spectroscopic measurements on this material and open new perspectives on the prospect of realizing quantum spin liquids in d5 halides and oxides in general. Of particular interest is the Kitaev Hamiltonian on the honeycomb lattice[5], which is a mathematically well-understood two-dimensional model exhibiting various topological SL states. Heisenberg-type J couplings, by longer-range spin interactions, or by having crystallographically distinct Ir-Ir bonds with dominant J’s on some of those, if not a combination of these factors[14,15,16,17]
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