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|Date and time:||10th Apr. (Tue.) 14:00 ` 15:00|
|Place:||SPring-8, "HOUKOUKAN" seminar room|
|Title:||Search for spin liquids in kagome and pyrochlore materials|
|uา:||Harald O. Jeschke ณ๖iชRๅwูช์๎bศwคj|
|Speaker:||Prof. Harald O. Jeschke (Research Institute for Interdisciplinary Science, Okayama University)|
Herbertsmithite ZnCu3(OH)6Cl2 is one of the best candidates for a quantum spin liquid; its Cu2+ ions form a kagome lattice. With half-filled Cu dx2-y2 bands, it is a Mott insulator. We have determined the parameters of the underlying Heisenberg Hamiltonian using density functional theory (DFT) methods. The tendency of herbertsmithite to some Cu/Zn disorder has led to the investigation of closely related kagome materials with different arrangement of kagome planes. Barlowite Cu4(OH)6FBr is a canted antiferromagnet. We have proposed to replace the interstitial Cu by a nonmagnetic metal ion in order to obtain another highly frustrated kagome material. Our prediction that such a material should be a very good spin liquid candidate has recently been confirmed experimentally.
An interesting polymorph of herbertsmithite is kapellasite which orders magnetically and has a ferromagnetic nearest neighbour exchange coupling. We discuss the positioning of kapellasite ZnCu3(OH)6Cl2, haydeeite MgCu3(OH)6Cl2 and hypthetical CdCu3(OH)6Cl2 in the phase diagram of the J1-J2-J3 Heisenberg model. We find kapellasite and haydeeite to be near the boundaries between magnetically ordered and disordered phases, and we predict that moderate pressures could bring the materials into the paramagnetic regime. We also investigate the low-temperature phase of the recently synthesized Lu2Mo2O5N2 material, a rare realization of an S = 1/2 three-dimensional pyrochlore Heisenberg antiferromagnet in which Mo5+ are the S = 1/2 magnetic species. Using density functional theory, we find that the compound is well described by a Heisenberg model with exchange parameters up to third nearest neighbors. The analysis of this model via the pseudofermion functional renormalization group method reveals paramagnetic behavior down to a temperature of at least T = |θCW|/100, in agreement with the experimental findings hinting at a possible three-dimensional quantum spin liquid.
Toru Sakai(University of Hyogo, QST SPring-8)|
Kenji Tsutsui(QST Pring-8)
Hiroki Nakano(University of Hyogo)