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Spin dynamics in the pyrochlore Yb2Ti2O7

Mercredi 6 mai 2015 14:00 - Duree : 1 heure
Lieu : ILL 4, Seminar Room, 71 avenue des Martyrs - Grenoble

Orateur : Julien ROBERT (Institut Néel, Grenoble)

Abstract : The static and dynamical correlations of the quantum spin liquid candidate Yb2Ti2O7 have been investigated by inelastic neutron scattering experiments on a single crystal. In this XXZ system, short range spin-ice like correlations settles around T0 2K, giving rise to rods of diffuse scattering along high symmetry directions [1]. Recent experiments reported that these correlations coexist with a long range canted ferromagnetic order with a strongly reduced static moment below Tc=265mK (ie far below the Curie Weiss temperature) [2], such that the exact nature of the ground-state of Yb2Ti2O7 remains puzzling [1-3].

In this work, focusing on Tc < T < T0 regime, we show that the short range correlations below T0 come along with non-conventional excitations, and that this dynamics does not evolve down to Tc. Excitations spectra are characterized by a very broad and almost flat dynamical response which extends up to 1-1.5 meV, coexisting with a quasi-elastic response or not, depending on the wave-vector [4]. Although classical mechanics qualitatively captures some of the experimental observations [4,5], we show that it fails to reproduce our excitation spectra. In particular, classical spin dynamics simulations predict an energy scale twice smaller than the experimental observations. These results suggest that the spin dynamics of Yb2Ti2O7 is governed by quantum fluctuations, and that the observed spectra rather correspond to a continuum of deconfined spinons as expected in quantum spin liquids, than simple paramagnons. The careful determination of the exchange tensors, which places Yb2Ti2O7 close to a FM/AFM phase boundary [4,5], further suggests that this quantum dynamics arise from competing FM and AFM correlations.

[1] Bonville et al. arXiv:0306470 (2003) ; Thompson et al. PRL 106, 187202 (2011) ; Ross et al. PRB 84, 174442 (2011) ; Chang et al. Nature Comm. 3, 992 (2012) ; [2] D’Ortenzio PRB 88, 134428 (2013) ; Lhotel et al. PRB 89, 224419 (2014) ; Chang et al. PRB 89, 184416 (2014) ; [3] Applegate et al. PRL 109, 097205 (2012) ; [4] J. Robert, E. Lhotel, S. Guitteny, C. Decorse, B. Canals, I. Mirebeau, S. Petit, in preparation. [5] Yan et al., arXiv:1311.3501 (2013)

Participants who have no badges allowing entrance to the ILL-ESRF site are kindly requested to give their names to Laurence Tellier tellier@ill.fr.

Discipline évènement : (Physique)
Entité organisatrice : (ILL)
Nature évènement : (Séminaire)
Evènement répétitif : (General ILL Seminar - College IV)
Site de l'évènement : Polygone scientifique

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