[Triumf-seminars] TRIUMF Seminar today at 14:00

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Date/Time: Fri 2005-06-24 at 14:00

Location:  Auditorium          

Speaker:   Hiroshi Kageyama (Department of Chemistry, Kyoto University)

Title:     Spin-Liquid States in Two-Dimensional Frustrated Quantum Spin Systems

Abstract: In low-dimensional quantum spin systems with geometrical frustration, spin-liquid states with short-range spin correlation have been sometimes achieved, instead of conventional long-range magnetic ordering. My talk will deal with two layered oxides, SrCu2(BO3)2 and (CuCl)LaNb2O7, both of which have the spin-liquid ground state with a finite energy to the lowlying excited state.
The structure of S=1/2 Cu2+ ions in SrCu2(BO3)2 is topologically equivalent to the Shastry-Sutherland model that is known to have the exactly solvable dimer singlet  ground state. One of the most interesting features in SrCu2(BO3)2 is the appearance of the quantized plateaus in the magnetization curve at low temperatures that is analogous to the metal-insulator transition in electron systems [1]. The NMR experiments under high magnetic field have clarified the spin structure at the 1/8 plateau phase [2]. The results of recent pressure experiments will be demonstrated if there is time.
(CuCl)LaNb2O7 with the S=1/2 square lattice is prepared by the topotactic ion-exchange reaction starting from a non-magnetic mother compound RbLaNb2O7. The magnetic susceptibility and inelastic neutron scattering studies have revealed the spin-liquid ground state with the gap of 2.3 meV [3]. As in the case of SrCu2(BO3)2 [4], the triplet excitation is almost dispersionless, probably due to the strong frustration. The origin of the spin-liquid formation will be discussed.

[1] Kageyama et al., Phys. Rev. Lett. 82 (1999) 3168.
[2] Kodama et al., Science 298 (2002) 395.
[3] Kageyama et al., J. Phys. Soc. Jpn. 74 (2005) 1702.
[4] Kageyama et al., Phys. Rev. Lett. 84 (2000) 5876.


Stimulants available 15 minutes before the talk.

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