Pseudospin exchange interactions ind7cobalt compounds: Possible realization of the Kitaev model

Abstract

The current efforts to find the materials hosting Kitaev model physics have been focused on Mott insulators of d 5 pseudospin-1/2 ions Ir 4+ and Ru 3+ with t 5 2g (S = 1/2, L = 1) electronic configuration. Here we propose that the Kitaev model can be realized in materials based on d 7 ions with t 5 2g e 2 g (S = 3/2, L = 1) configuration such as Co 2+ , which also host the pseudospin-1/2 magnetism. Considering possible exchange processes, we have derived the d 7 pseudospin-1/2 interactions in 90 • bonding geometry. The obtained Hamiltonian comprises the bond-directional Kitaev K and isotropic Heisenberg J interactions as in the case of d 5 ions. However, we find that the presence of additional, spin-active eg electrons radically changes the balance between Kitaev and Heisenberg couplings. Most remarkably, we show that the exchange processes involving eg spins are highly sensitive to whether the system is in Mott (U < ∆) or charge-transfer (U > ∆) insulating regime. In the latter case, to which many cobalt compounds do actually belong, the antiferromagnetic Heisenberg coupling J is strongly suppressed and spin-liquid phase can be stabilized. The results suggest cobalt-based materials as promising candidates for the realization of the Kitaev model. arXiv:1710.10193v2 [cond-mat.str-el]

Interplay between Kitaev interaction and single ion anisotropy in ferromagnetic CrI3 and CrGeTe3 monolayers

“…Interestingly, finding finite Kitaev interaction in Cr-3d based CrI 3 and CrGeTe 3 compounds would enlarge the types of systems possessing such interaction, not only from 4d or 5d to 3d transition-metal-based insulators, but also from S = 1/2 to S = 3/2 systems. Such broadening is in-line with recent theoretical predictions of Kitaev interaction in d 7 or 3d systems 15,16 .…”

Unifying description of competing orders in two-dimensional quantum magnets

“…We note that at a qualitative level, the discrepancies from spin wave theory are connected to low energy spectral weight at the M points, which are recovered within the QED 3 theory, where they arise from fermion bilinears. It has been pointed out that additional terms beyond the Heisenberg interaction may be present in these materials [72] which help stabilize a spin liquid state. The transition metal dichalcogenide 1T-TaS 2 has also been proposed as a quantum spin liquid where the spin degrees of freedom reside on clusters that form a triangular lattice [73].…”

Experimental identification of quantum spin liquids

“…17 Recently, Kitaev physics has also been discussed in ions which have the d 7 configuration, such as Co 2+ , where the combination of S = 3/2 and orbital moment L eff = −1 can also give rise to a j eff = 1/2 state. 91 Moreover, the possibility of realizing QSL physics in a square lattice featuring competing magnetic interactions (for example, competing nearest-and next-nearestneighbour exchange couplings) has also been widely discussed in recent years. [92][93][94] In some occasions, there may be some other interactions that disturb the QSL state, making the material not an ideal QSL but proximate to it.…”