Introduce: Selene MOR, Università Cattolica del Sacro Cuore

Interviene:
Dr. Christopher W. NICHOLSON, University of Fribourg (Switzerland)

The study of emergent phenomena in quantum materials continues to produce exciting results and fundamental insights. In order to untangle the coupled degrees of freedom responsible for such behaviour requires a range of approaches and techniques. A powerful method that has developed rapidly over the last 20 years is resonant inelastic X-ray scattering (RIXS) [1], which harnesses the power of synchroton sources to probe a range of properties, from collective phonons and magnons, to local crystal symmetries. Recent developments in the field include extending the RIXS technique into the femtosecond domain using X-ray free electron laser (XFEL) sources, further exploiting its potential to probe complex behaviour. In this presentation I will demonstrate some of the versatility of the RIXS technique by briefly addressing two material systems. In the first case I will present RIXS data on superconducting oxide thin films that display interfacial charge ordering [2]. Comparing data obtained under different scattering conditions reveal this order has an unusual orbital symmetry, which contrasts with previous observations in the cuprates. The presence of tuneable interfacial charge transfer implies that interface engineering may allow direct control over this and similar behaviour. In the second case I will show femtosecond RIXS results from a magnetically frustrated insulator. In these challenging experiments, excitation across the charge gap produces a reduction of localised spin correlations that cannot be fully explained by a purely thermal heating of the lattice, hinting at the decoupling of lattice and magnetic channels on ultrafast timescales. These results help set the scene for future investigations at next generation XFEL facilities currently under development.

[1] Ament et al., Rev. Mod. Phys. 83, 705 (2011)
[2] Gaina et al, arXiv:2007.15894 (2020); in press at npj Quantum Materials (2021)

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