Interacting degrees of freedom – the lattice-dynamics point of view
Dr. Frank Weber
Neutron Scattering Group Leader
Institute for Solid-State Physics
Karlsruhe Institute of Technology
Date & Time
Room 7-37, Haking Wong Building, HKU
Many of the remarkable properties of quantum materials result from strong interaction among the electronic, magnetic and lattice degrees of freedom and the rich variety of ordered states, including superconductivity, that emerge as a consequence, often in close proximity to each other in a given phase diagram. Reporting on investigations in various such materials, we focus on the lattice dynamical properties via momentum-resolved phonon spectroscopy, which is traditionally the domain of inelastic neutron scattering. However, this field has tremendously benefitted from the development of inelastic x-ray scattering with energy resolution down to 1 milli-electronvolt. After a short comparison of state-of-the-art inelastic neutron and x-ray scattering experiments, I will review work using both neutrons and x-rays to investigate phonons in:
1. the seminal charge-density-wave system and superconductor 2H-NbSe2 ;
2. the iron-based superconductor Ba(Fe0.94Co0.06)2As2 featuring strong nematic fluctuations ;
3. the temperature-activate paramagnet FeSi exhibiting spin-phonon interaction 
 F. Weber et al., Physical Review Letters 107, 107403 (2011).
 F. Weber et al., Physical Review B 97, 235122 (2018).
 S. Krannich et al., Nature Communications 6, 8961 (2015).