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Séminaire Magnétisme non conventionnel

Jeudi 19 Octobre à 14h00,
Salle Remy Lemaire K223

Orateur : Dalila BOUNOUA (ICMMO, Orsay)
"Spin and Lattice Dynamics in the Pristine and S=0 doped Quasi-1D Spin Chains Cuprate SrCuO2 Probed by Inelastic Neutron Scattering"


We investigate the finite size effect on the magnetic excitations and phonons spectra of the quasi-1D spin chains system SrCuO2. This cuprate crystallizes in the orthorhombic space group Cmcm, and carries zigzag spin 1⁄2 chains of Cu2+ along the c-axis. Despite the presence of a frustrated ferromagnetic superexchange interaction within the chains, SrCuO2 behaves as linear antiferromagnetic spin chains compound rather than a two-leg ladder one. Consequently, its magnetic excitations spectrum consists in a gapless Des Cloiseaux-Pearson two-spinon continuum and the material is described as a Tomonaga-Luttinger spin liquid. On the other hand, SrCuO2 belongs to the family of the strongly correlated Mott insulators and exhibits anisotropic heat transport properties along the direction of the Cu-O chains, where heat is carried by phonons and spinon [1]. This gives rise to various scattering channels, involving both quasi-particles and defects, which are highly relevant to the heat conduction process.
In this work, we probe the spinon-defects and phonons-defects scattering mechanisms, through the introduction of fractional amounts of S=0 impurities within the chains, in order to further correlate them to the resulting transport properties. To this aim, single crystals of the pristine and 1% Mg, Zn, Pd or La-doped SrCuO2 have been grown by the traveling solvent floating zone method. The chemical, structural and magnetic characterizations of the compounds will be presented. Furthermore, inelastic neutron scattering measurements have been carried out in order to determine the doping effect on the spin excitations spectra of the substituted compounds, and follow phonons modes propagating longitudinally along Q(0 0 L), and transversally along Q(H 0 2) and Q(2 0 L). Our results show systematic spin pseudogaps opening in the magnetic excitations spectra of the substituted materials [2,3]. Additionally, the longitudinal phonon spectra highlight a strong spinon-phonon interaction leading to a decay of the acoustic phonon spectral weight afterwards [4] ; whereas a phason-like dispersion emerges on the transverse phonon spectra along Q(H 0 2), suggesting the existence of an out of phase shearing motion between the chains and the overall crystal lattice. Results from INS will be discussed and linked to heat transport measurements.
[1] A.V. Sologubenko, K. Gianno, H.R. Ott, A. Vietkine, A, A. Revcolevschi, Phys. Rev. B, 64, 054412 (2001).

[2] D. Bounoua, R. Saint-Martin, S. Petit, P. Berthet, F. Damay, Y. Sidis, F. Bourdarot, L. Pinsard-Gaudart, Phys. Rev. B, 95, 224429 (2017).

[3] Y. Utz, F. Hammerath, R. Kraus, T. Ritschel, J. Geck, L. Hozoi, J. van den Brink, A. Mohan, C. Hess, K. Karmakar, S. Singh, D. Bounoua, R. Saint-Martin, L. Pinsard-Gaudart, A. Revcolevschi, B. Büchner, and H.-J. Grafe, Phys. Rev. B 96, 115135 (2017).

[4] D. Bounoua, R. Saint-Martin, S. Petit, F. Bourdarot, L. Pinsard-Gaudart. Physica B : Condens. Matter, (Under review).

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