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|Date and time:||6th November (Fri.) 16:00`|
|Place:||SPring-8, "HOUKOUKAN" seminar room|
|Title:||Towards a phase diagram for the Kagome antiferromagnet with Dzyaloshinskii-Moriya interactions?|
|Speaker:||Dr. Oliviér Cépas@(Institut Néel, Grenoble)|
With the recent discovery of a magnetic compound that does not order down to the lowest temperatures, the question of a putative ``spin-liquid'' phase has resurfaced. The herberthsmithite ZnCu3(OH)6Cl3 is a model compound of strongly interacting spins S = 1/2 that has the geometry of the kagome lattice. Is the ground state a spin-liquid (possibly ``algebraic'') or does it have some hidden long-range order like in a valence bond crystal?
In reality, small corrections of spin-orbit origin -Dzyaloshinskii-Moriya interactions- are inevitably present (and allow to test -at least theoretically- the stability of the above mentioned phases). I will show that such an interaction destroys the moment-free phase and induces Néel order above a finite quantum critical point. In fact on the basis of Schwinger boson mean-field theory additional phases are expected, but not seen in exact diagonalization studies.
I will discuss the results in the view of the current theories of the quantum kagome antiferromagnet (RVB, valence bond crystal...) and argue that the magnetic properties of ZnCu3(OH)6Cl3 could be controlled by the proximity to this critical point. However, the nature of the moment-free phase (spin-liquids, valence bond crystals?) is still debated and I will show that it is in principle possible to look for such hidden symmetries using Raman scattering.