Neutron and resonant inelastic x‐ray scattering studies of multiferroic langasite and superconducting cuprates

Abstract

In this talk, we will begin by a general description focused on how the neutron (NS) and resonant inelastic x‐ray scattering (RIXS) can provide comprehensive and complementary information about the static and dynamical properties of strongly correlated systems. We will go through two specific examples where the NS and RIXS have been crucial techniques:

• 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 Bi₂Sr₂CaCu₂O_8+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 wave-vector and intersect with bond-stretching phonons, causing anomalously enhanced phonon intensity at a wave-vector away from the CDW wave-vector [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).

Laboratoire Léon Brillouin