Publication details

Exchange interactions in d5 Kitaev materials: From Na2IrO3 to α−RuCl3

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Year of publication 2022
Type Article in Periodical
Magazine / Source Physical Review B
MU Faculty or unit

Faculty of Science

Keywords Exact diagonalization; Kitaev model; Honeycomb lattice; Strongly correlated systems; Magnetic interactions; Magnetism; Magnons; Spin liquid
Description We present an analytical study of the exchange interactions between pseudospin one-half d5 ions in honeycomb lattices with edge-shared octahedra. Various exchange channels involving Hubbard U, charge-transfer excitations, and cyclic exchange are considered. Hoppings within t2g orbitals as well as between t2g and eg orbitals are included. Special attention is paid to the trigonal crystal field ? effects on the exchange parameters. The obtained exchange Hamiltonian is dominated by ferromagnetic Kitaev interaction K within a wide range of ?. It is found that a parameter region close to the charge-transfer insulator regime and with a small ? is most promising to realize the Kitaev spin liquid phase. Two representative honeycomb materials Na2IrO3 and ?-RuCl3 are discussed based on our theory. We have found that both materials share dominant ferromagnetic K and positive nondiagonal ? values. However, their Heisenberg J terms have opposite signs: AFM J>0 in Na2IrO3 and FM J<0 in ?-RuCl3. This brings different magnetic fluctuations and results in their different magnetization behaviors and spin excitation spectra. Proximity to FM state due to the large FM J is emphasized in ?-RuCl3. The differences between the exchange couplings of these two materials originate from the opposite ? values, indicating that the crystal field can serve as an efficient control parameter to tune the magnetic properties of d5 spin-orbit Mott insulators.
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