Abstract
What is the correct low-energy spin Hamiltonian description of alpha-RuCl_{3}? The material is a promising Kitaev spin liquid candidate, but is also known to order magnetically, the description of which necessitates additional interaction terms. The nature of these interactions, their magnitudes and even signs, remain an open question. In this work we systematically investigate dynamical and thermodynamic magnetic properties of proposed effective Hamiltonians. We calculate zero-temperature inelastic neutron scattering (INS) intensities using exact diagonalization, and magnetic specific heat using a thermal pure quantum states method. We find that no single current model satisfactorily explains all observed phenomena of alpha-RuCl_{3}. In particular, we find that Hamiltonians derived from first principles can capture the experimentally observed high-temperature peak in the magnetic specific heat, while overestimating the magnon energy at the zone center. In contrast, other models reproduce important features of the INS data, but do not adequately describe the magnetic specific heat. To address this discrepancy we propose a modified ab initio model that is consistent with both magnetic specific heat and low-energy features of INS data.
Highlights
Quantum spin liquids (QSL) are long-sought-after states of matter without magnetic order, but with nontrivial topological and potentially exotic properties.[1,2] Much of the search has been focused on frustrated lattice systems,[3,4] but in an important development in 2006 Kitaev[5] introduced a novel exactly solvable paradigmatic QSL with bond-directional Ising terms on the bipartite honeycomb lattice
To untangle the roles and effects of different interaction terms, we focus on a minimal qK 1ffiJffi21ÀffiffiffiþffiffiΓffiffi1ffiKffiffiÀffi21ffiffiffiþffiΓffiffi01ffiffiΓffiÀffi21ffiffiffiþffiJffiffi3ffiffiÀffiffiΓffiffi01ffiffimÁffiffi2ffiffioffiþffidffiffiffieffiJffilffi23.ffi
We focus on (i) the positions ωΓ and ωM of the initial spin wave peaks in the inelastic neutron scattering (INS) intensity at the Γ and M points, respectively, (ii) the shape of the neutron scattering intensity map (IM) in momentum space integrated over 1⁄24:5; 7:5 meV, and (iii) the position of the high-temperature peak in the magnetic specific heat
Summary
Quantum spin liquids (QSL) are long-sought-after states of matter without magnetic order, but with nontrivial topological and potentially exotic properties.[1,2] Much of the search has been focused on frustrated lattice systems,[3,4] but in an important development in 2006 Kitaev[5] introduced a novel exactly solvable paradigmatic QSL with bond-directional Ising terms on the bipartite honeycomb lattice. Na2IrO315–17 and α-RuCl318–21 both develop a zigzag order, as illustrated in Fig. 1a, while Li2IrO3 displays an incommensurate spiral order.[22]
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