M. Taillefumiera, J. Robertb, B. Canalsc, C. Henleyd, R. Moessnere
a Institute für Theoretische Physik, W. Goethe Universität, Max-Von-Laue Strasse 1, 60438 Frankfürt am Main
b Laboratoire Léon Brillouin - CEA Saclay, bât. 563, F-91191 Gif-sur-Yvette cedex, France
c Institut Néel - 25 avenue des Martyrs, bât. K, BP 166, 38042 Grenoble cedex 9, France
d Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853-2501, USA
e Max Planck Institute for the Physics of Complex Systems, Nothnitzer Str. 38, 01187 Dresden
By combining monte carlo and spin dynamics simulations, we investigate the precessionnal dynamics of the classical kagome antiferromagnet through the calculation of the dynamical structure factor S(Q, t). Recently, evidences for spin wave like excitations in the two distincts spin liquid (T > T0) and coplanar (T < T0) low temperature regimes – whose temperature ranges are given by the entropically driven onset of spin plane coplanarity at T0/J ~ 5 x 10-3 – has been given  . However, only a little is known about the longer time scales describing the ﬂuctuations around the ground-state manifold.
Here, to capture how such propagative excitations arise in spite of short-ranged static correlations, we give more insight about this relaxationnal dynamics and establish in particular the temperature and wave-vector dependence of the lifetime of locally ordered states. Although the inﬁnite components spins model  qualitatively accounts for the dynamical properties in the spin liquid regime (T/J > 5 x 10-3 ), we show at lower temperature that the entropic selection (i) leads to strongly diﬀerent dynamical correlations for the in-plane and out-of-plane spin components below the transition (the out-of-plane ﬂuctuations being governed by weathervane-modes), and (ii) almost suppresses the diﬀusive behavior observed in the cooperative regime in favor of mainly propagative spin transfers .
We furthermore show that the powder averaged spectrum is overwhelmed by these spin ﬂuctuations, pointing out that the propagative spin waves evidenced in  would be hardly discernible in powder samples down to very low temperatures, as observed experimentally .
 J. Robert, B. Canals, V. Simonet and R. Ballou, Phys. Rev. Lett. 101, 117207 (2008).
 P. H. Conlon and J. T. Chalker, Phys. Rev. Lett. 102, 237206 (2009).
 M. Taillefumier, J. Robert, B. Canals, C. Henley, and R. Moessner, in preparation (2012).
 B. Fåk, F. C. Coomer, A. Harrison, D. Visser, and M. E. Zhitomirsky, EPL 81, 17006 (2008).