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Séminaire MCBT : Mardi 8 juin 2021 à 11h

Manila Songvilay, équipe MagSup

En visio sur (webcast @) : https://univ-grenoble-alpes-fr.zoom.us/my/matteo.dastuto

Title: « Kitaev interactions in cobalt honeycomb-lattice oxides »

Abstract: The recent Kitaev model (2006) provides an exact model to achieve a quantum spin liquid ground state in a 2D honeycomb lattice system through Ising-like bond-dependent interactions [1]. While first considered as a toy model, a theoretical work from Jackeli and Khaliullin has paved the way toward the realization of Kitaev physics in bulk materials. They first showed that bond-dependent interactions can be achieved through the interplay between crystal field, spin-orbit coupling and bond geometry using 4d and 5d transition metal ions, that exhibit a strong spin-orbit coupling [2]. Since then, a significant amount of experimental works have focused on iridate and ruthenate compounds to find a suitable candidate material [3].
Co2+ ions in an octahedral crystal field stabilize a jeff = 1/2 ground state with an orbital degree of freedom and have been more recently put forward for realizing Kitaev interactions [4], a prediction we have tested by investigating spin dynamics in two cobalt honeycomb lattice compounds, Na2Co2TeO6 and Na3Co2SbO6, using inelastic neutron scattering. We used linear spin wave theory to show that the magnetic spectra can be reproduced with a spin Hamiltonian including a dominant Kitaev nearest-neighbor interaction, weaker Heisenberg interactions up to the third neighbor, and bond-dependent off-diagonal exchange interactions [5]. Beyond the Kitaev interaction that alone would induce a quantum spin liquid state, the presence of these additional couplings is responsible for the zigzag-type long-range magnetic ordering observed at low temperature in both compounds. These results provide evidence for the realization of Kitaev-type couplings in cobalt-based materials, despite hosting a weaker spin-orbit coupling than their 4d and 5d counterparts, and therefore open to new possibilities for future new material prospection.
Références :
[1] A. Kitaev, Annals of Physics 321, 2-111 (2006)
[2] G. Jackeli and G. Khaliullin, Physical Review Letters 102, 017205 (2009)
[3] S. M. Winter et al., J. Phys. : Condens. Matter 29, 493002 (2017)
[4] H. Liu and G. Khaliullin, Physical Review B 97, 014407 (2018); R. Sano et al., Physical Review B 97, 014408 (2018); H. Liu et al., Physical Review Letters 125, 047201 (2020)
[5] M. Songvilay et al., Physical Review B 102, 224429 (2020)