title: Relevance of the Heisenberg-Kitaev model for the honeycomb lattice iridates A2IrO3.
abstract: Combining thermodynamic measurements with theoretical calculations we demonstrate that the iridates A2IrO3 (A=Na, Li) are magnetically ordered Mott insulators where the magnetism of the effective spin-orbital S=1/2 moments can be captured by a Heisenberg-Kitaev (HK) model with interactions beyond nearest-neighbor exchange. Experimentally, we observe an increase of the Curie-Weiss temperature from θ≈-125  K for Na2IrO3 to θ≈-33  K for Li2IrO3, while the ordering temperature remains roughly the same T(N)≈15  K. Using functional renormalization group calculations we show that this evolution of θ and T(N) as well as the low temperature zigzag magnetic order can be captured within this extended HK model. We estimate that Na2IrO3 is deep in a magnetically ordered regime, while Li2IrO3 appears to be close to a spin-liquid regime.
authors.affiliation: Indian Institute of Science Education and Research Mohali, Sector 81, SAS Nagar, Manauli PO 140306, India.
authors.forename: Yogesh
authors.initials: Y
authors.lastname: Singh
authors.forename: S
authors.initials: S
authors.lastname: Manni
authors.forename: J
authors.initials: J
authors.lastname: Reuther
authors.forename: T
authors.initials: T
authors.lastname: Berlijn
authors.forename: R
authors.initials: R
authors.lastname: Thomale
authors.forename: W
authors.initials: W
authors.lastname: Ku
authors.forename: S
authors.initials: S
authors.lastname: Trebst
authors.forename: P
authors.initials: P
authors.lastname: Gegenwart