| 日時: | 平成24年10月29日(月) 16:00〜 |
| Date and time: | 29th October (Mon.) 16:00〜 |
| 場所: | SPring-8, 萌光館 |
| Place: | SPring-8, "HOUKOUKAN" seminar room |
| Title: | Effective model and spin/charge ordering in Pd(dmit)2 salts |
| 講演者: | 妹尾仁嗣 氏 （理研） |
| Speaker: | Dr. Hitoshi Seo (RIKEN) |
| Abstract: |
Among the family of beta'-type X[Pd(dmit)2]2 (X: monovalent cation) salts [1], many become a dimer-type Mott insulator and then at low temperatures they show magnetic order or spin-liquid behavior. On the other hand, pressure or chemical modification brings about competition with metallic/superconducting states, and also with a peculiar charge ordering involving multi-orbitals. In this study, we construct an effective low-energy model which take into account the multi-orbital degree of freedom, and investigate their electronic states systematically.
We take fragments of molecular orbital (fragment MO; fMO) as a basis set of the model, of which HOMO and LUMO of the Pd(dmit)2 molecule are composed by linear combinations; each fMO becomes nearly localized on one of the dmit ligands. The inter-fMO transfer integrals are obtained for a series of salts X = EtxMe4-xZ (x = 0-2, Z = P, As, Sb) by fitting to the first-principles band calculations [2]. We find that all the intra-dimer transfer integrals, including the diagonal ones, are appreciably large (0.2-0.3eV); this results in a modification of the orbital scheme in strongly dimerized [Pd(dmit)2]2 discussed in the literatures, then to the effective dimer model. We calculate possible spin and charge ordering based on mean-field approximation to the extended Hubbard model incorporating the fitted parameters.
This work is in collaboration with T. Tsumuraya (RIKEN & NIMS), T. Miyazaki (NIMS), M. Tsuchiizu (Nagoya), and R. Kato (RIKEN).
[1] For reviews, R. Kato, Chem. Rev. 104 (2004) 5319; M. Tamura and R. Kato, Sci. Technol. Adv. Mater. 10 (2009) 024304; K. Kanoda and R. Kato: Annu. Rev. Condens. Matter Phys. 2, 167 (2011).
[2] T. Miyazaki and T. Ohno, Phys. Rev. B 59 (1999) 5269; T. Tsumuraya, H. Seo, M. Tsuchiizu, R. Kato, and T. Miyazaki, in preparation.