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|Date and time:||20th May (Fri.) 16:00`|
|Place:||SPring-8, "HOUKOUKAN" seminar room|
|Title:||Nontrivial ferrimagnetism in the ground state of low-dimensional frustrated Heisenberg spin systems|
|uÒ:||ºì vN (ºÉ§§åw¨¿w¤È)|
|Speaker:||Dr. Tokuro Simokawa (Graduate School of Material Science, University of Hyogo)|
Ferrimagnetism is a fundamental phenomenon that is defined as a state which is consisted of an antiferromagnetic spin order with spontaneous ferromagnetic magnetization. A typical ferrimagnetic state appears in the ground state of (S, s)=(1,1/2) antiferromagnetic mixed chain, in which two different spins in each unit cell are arranged alternately in a line. The occurrence of such ferrimagnetism is understood within the Marshall-Lieb-Mattis theorem . This type of ferrimagnetism is called "Lieb-Mattis (LM) type". In the LM type ferrimagnetism, the situation that more spins than one in each unit cell are included is an essential role for the appearance of the ferrimagnetisms. Though it has long been believed that multi-sublattice structure is requisite for the occurrence of ferrimagnetism, quite recently we discovered a case of the occurrence of ferrimagnetism in the ground state of the S=1/2 Heisenberg frustrated spin chain in spite of the fact that a unit cell of the chain includes only a single spin, namely, it has no sublattice structure. From our calculations by exact-diagonalization method and density matrix renormalization group method, we find that there are two types of ferrimagnetic phases of this model: the phase of LM type and the phase of non-Lieb-Mattis (NLM) type which is found in several one-dimensional frustrated systems. I would like to talk about details of the results by numerical calculations.
In addition, we find that the NLM ferrimagnetic state can be realized in the spatially anisotropic two-dimensional kagome lattice system.
I would also discuss the behavior of the NLM ferrimagnetism by our investigation of the ground state properties of the S=1/2 kagome stripe lattice that is a part of the two-dimensional kagome lattice.
 E. Lieb and D. Mattis: J. Math. Phys. 3 (1962) 749.
 W. Marshall: Proc. Roy. Soc. A 232 (1955) 48.
 T. Shimokawa and H. Nakano: J. Phys. Soc. Jpn. 80 (2011) 043703
 K. Hida: J. Phys.: Condens. Matter 19 (2007) 145225.
 H. Nakano, T. Shimokawa and T. Sakai: J. Phys. Soc. Jpn. 80 (2011) 033709
 T. Shimokawa and H. Nakano: proceedings of the International Conference on Frustration in Condensed Matter in Sendai.