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Magnetic excitations studied by x-rays

Mardi 15 mars 2016 11:00 - Duree : 1 heure
Lieu : Salle "Louis Weil" E424 - Institut Néel -bâtiment E, 3ème étage, CNRS Polygone scientifique, 25 rue des martyrs, 38000 Grenoble

Orateur : Marco MORETTI SALA (ESRF)

Correlated systems show a variety of interactions involving charge, spin and orbital degrees of freedom of the electrons, which give rise to a number of fascinating properties. The m ost prominent example is probably the phenomenon of high-Tc superconductivity in layered cuprates. The phase diagram of high-Tc superconducting cuprates features the suppression of long-range antiferromagnetic order concomitant to the emergence of superconductivity, which shows a domelike behavior upon doping increase [1]. Despite the loss of long range magnetic order, it was found that antiferromagnetic fluctuations survive up to the so-called overdoped regime [2]. However, the link between the magnetism and superconductivity still remains object of debate. Spin waves - or magnons - are the elementary excitations of a magnetically ordered lattice. Conventionally, these are best studied by inelastic neutron scattering techniques. However, neutron experiments fall short, for example, in the case of very small sample volumes (tiny crystals, thin films) or sample containing strong neutron absorbers (like Ir). In such cases, it was useful to realize that magnetic dynamics could be probed as well by x-ray scattering techniques, in a way complementary to neutrons. I will briefly introduce the technique of resonant inelastic x-ray scattering (RIXS) for the study of elementary excitations in solids as a function of transferred momentum and polarization. The discussion will then be focused on the mechanism giving rise to "spin-flip" excitations in L2,3 edge RIXS of transition metals. It relies on the spin-orbit coupling of the intermediate state probed during the RIXS process as it can be easily understood within the framework of a single ion model [3]. Key experimental results are finally reviewed, with emphasis to the case of antiferromagnetic insulating cuprates (Cu L2,3 [4] and K edges [5], O K edge [6]) and iridates (Ir L2,3 edge [7]).

[1] see, for example, E. Fradkin and S. A. Kivelson, Nature Physics 8, 864 (2012).

[2] M. Le Tacon et al., Nature Physics 7, 725 (2011) ; Phys. Rev. B 88, 020501(R) (2013) ; M. P. M. Dean et al., Nature Materials 12, 1019 (2013).

[3] L. J. P. Ament, Phys. Rev. Lett., 103, 117003 (2009).

[4] L. Braicovich et al., Phys. Rev. Lett., 104, 077002 (2010).

[5] J. P. Hill et al., Phys. Rev. Lett. 100, 097001 (2008).

[6] V. Bisogni et al., Phys. Rev. B, 85, 214527 (2012).

[7] J. Kim et al. Phys. Rev. Lett. 108, 177003 (2012).

Contact : emilio.lorenzo@neel.cnrs.fr

Discipline évènement : (Physique)
Entité organisatrice : (Institut Néel / MCBT)
Nature évènement : (Séminaire)
Evènement répétitif : (Séminaire MCBT)
Site de l'évènement : Polygone scientifique

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