Séminaire de groupe
|The kagome antiferromagnet: a chiral spin liquid ?|
|jeudi 21 février 2013 , 14h00|
|Salle de séminaire du groupe de Physique Statistique|
At the classical level, the ground state of the kagome antiferromagnet is highly degenerate. Thermal fluctuations favorize planar ground states and until now, quantum fluctuations were supposed to do the same as indicates a first order spin wave expansion. The Schwinger boson mean-field approach takes into account a large amount of quantum effects and can describe both long range ordered spin states and spin liquids (what is supposed to be the quantum kagome antiferromagnet). Until now, it has only been applied to states derived from classical planar spin states. By allowing spontaneous chiral symmetry breaking, we show that at T=0 a chiral (non planar) phase is indeed more stable than any other phases studied up to now, opening new possibilities for the quantum ground state. We will discuss the evolution of the phase diagram with the value of the spin from quantum spins to classical ones. For quantum spins we will confront our results to various results obtained with exact diagonalizations: symmetries of the exact spectra, properties of the spin-1/2 excitations, dynamical structure factors.