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|Date and time:||17th Oct. (Fri.) 16:00`|
|Place:||SPring-8, "HOUKOUKAN" seminar room|
|Title:||Theory of nonmagnetic state in dimer-Mott insulating systems|
|Speaker:||Dr. Makoto Naka (RIKEN)|
Quasi two-dimensional molecular compound κ-(ET)2Cu2(CN)3 is known as a dimer-Mott insulator and a candidate of quantum spin liquid materials . Recently, a relaxor-like dielectric anomaly is observed in this compound . This origin is thought to be a charge degree of freedom due to localization of a hole in one side of two ET molecules in a dimer. This result strongly suggests that this system should be recognized as a multi-orbital Mott insulating system. Here, we theoretically study the possibility of a gno magnetic long-range orderh coming from the charge degree of freedom inside the dimer. We start from the extended Hubbard model on a dimer-Mott system and derive a Kugel-Khomskii-type spin / charge pseudo-spin coupled model . This model is analyzed by using a mean-field approximation and spin-wave approximation. In the presence of a spin-charge coupling term, we find that a spin moment on the dimer is remarkably reduced and magnetic long-range orders become unstable due to a quantum fluctuation in a wide range of parameters .
 Y. Shimizu, K.. Miyagawa, K. Kanoda, M. Maesato, and G. Saito, Phys. Rev. Lett. 91 107001 (2003).
 M. Abdel-Jawad, I. Terasaki, T. Sasaki, N. Yoneyama, N. Kobayashi, Y. Uesu and C. Hotta, Phys. Rev. B 82 125119 (2010).
 M. Naka and S. Ishihara, J. Phys. Soc. Jpn. 79 063707 (2010).
 M. Naka, T. Watanabe, J. Nasu, and S. Ishihara, in preparation.