Invited Paper AC+MI-WeM3
Neutron and X-ray Scattering as a Probe of Complex Order in Actinides

Wednesday, November 9, 2016, 8:40 am, Room 103C

Neutron and X-ray scattering are powerful probes of complex ordering in the actinides, giving access to the spatial and temporal fluctuations of structural and electronic degrees of freedom. To demonstrate the vast array of different types of information obtainable using different scattering techniques, I will focus on the question of the elusive hidden order parameter in URu₂Si₂.

Innumerable different theories have been proposed for the nature of the hidden order [1], with a preponderance directed towards multipolar order. With this in mind I will discuss how X-ray Resonant Elastic Scattering has shown that no quadrupolar ordering is present [2], and future opportunities for probing higher order multipoles. I will also discuss the valence state, which is of vital significance for any multipolar model, and how this might be investigated by probing the f-states at the M-edges using Resonant X-ray Emission Spectroscopy.

More recently, there is a growing consensus pointing towards some electronic nematic state, resulting in an orthorhombic distortion [3,4,5]. Inelastic neutron and X-ray scattering experiments, which have searched for a change in the band structure associated with such a distortion, will be discussed.

[1] J.A. Mydosh and P.M. Oppeneer, Rev. Mod. Phys.83, 1301 (2011)

[2] H.C. Walker, et al., Phys. Rev. B83, 193102 (2011)

[3] R. Okazaki, et al., Science331, 439 (2011).

[4] S. Kambe, et al., Phys. Rev. Lett.110, 246406 (2013).

[5] S. Tonegawa et al., Nat. Comms. 5, 4188 (2014)