Transition metal compounds in which electrons from partially filed d-shells strongly interact with each other keep challenging the standard theory of solids as new, emergent exotic electronic orders are experimentally observed. Despite vastly different macroscopic properties, e.g. high temperature superconductivity (HTS), electronic nematicity or density waves to cite a few, the electronic phases encountered in these quantum materials can be almost degenerate and compete with each other within complex phase diagrams.

The underlying crystal lattice plays a crucial role that can be exploited to either tune the electronic states of a material (and thereby to learn more about the microscopic mechanisms underpinning their stabilization) or to monitor their electronic.

In the first part of the talk, I will show how the combination of pressure (hydrostatic or uniaxial) tuning and x-ray spectroscopy has been used in the course of the last decade to gain fresh insights on the properties of charge density waves (CDW) in high temperature superconducting cuprates [1-3].

The second part will focus on a different CDW material, BaNi2(As1-xPx)2, the nickel homologue to the Fe-based superconductors. There I will discuss how by carefully monitoring the lattice dynamics of, we have recently observed a new type of electronic nematicity, dynamical in nature, which exhibits a particularly strong coupling to the underlying crystal lattice. We argue that fluctuations between degenerate nematic configurations cause a splitting of phonon lines, without lifting degeneracies nor breaking symmetries, akin to spin liquids in magnetic systems[4].

References

[1] S. M. Souliou, et al. Phys. Rev. B 97 020503 (2018).

[2] H. H. Kim, S. M. Souliou et al. Science 362 1040 (2018).

[3] H. H. Kim, et al. Phys. Rev. Lett. 126 037002 (2021).

[4] Y. Yao, et al. Nature Communications 13 4535 (2022).