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Séminaire QUEST

Jeudi 09 novrembre à 9h30,
Salle Rémy Lemaire, K223

Oratrice : Laura CHAIX (Laboratoire Léon Brillouin)
"Neutron and resonant inelastic x‐ray scattering from multiferroic langasite and superconducting cuprates"


This talk will begin by a general introduction to the field of strongly correlated systems, including transition metal oxides that exhibit a large variety of cross-coupling phenomena such as multiferroicity and superconductivity. We will describe how the neutron (NS) and resonant inelastic x‐ray scattering (RIXS) provide comprehensive, energy and momentum resolved information about the ground state and excitation spectra of these materials. We will go through two specific examples where the NS and RIXS have yielded new insights :

- In the multi-chiral Fe-langasite, NS observations revealed that its magnetic picture was incomplete. Extinctions and gaps in the spin-waves spectrum were discovered as well as additional weak magnetic satellites. These features are explained by the loss of the 3-fold axis and the presence of single-ion anisotropy inducing a bunched modulation of the helical order. We will see that these small modulations have, in fact, large consequences on the understanding of the multiferroic properties of this intriguing compound [1].

- The low energy excitations in the heavily underdoped cuprate superconductor Bi2Sr2CaCu2O8+δ (Bi-2212) were investigated using ultrahigh energy resolution RIXS in the soft x-ray regime. In the quasi-elastic region, an incommensurate charge density wave (CDW) was observed, confirming the existence of a CDW in this compound. Importantly, this RIXS study revealed signatures of dispersive CDW excitations that emanate from the CDW wavevector and intersect with bond-stretching phonons, causing an anomalously enhanced phonon intensity at a wavevector away from the CDW wavevector [2]. Temperature dependent measurement will also be discussed.
We will conclude by giving some perspective topics where the use in parallel of these two complementary scattering techniques will be a great advantage.

[1] L. Chaix et al., Phys. Rev. B 93, 214419 (2016).
[2] L. Chaix et al., Nat. Phys. 13, 952–956 (2017).

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