Many complex materials display an interesting interplay between structural and electronic properties, which can be studied effectively under applied pressure. This talk will discuss three recent examples: (i) if a continuous structural phase transition is suppressed to low temperatures (e.g. [1]), low-energy vibrational excitations can arise that boost superconductivity and cause a linearly temperature dependent electrical resistivity. In aperiodic high-pressure host-guest structures, such as that found in high-pressure bismuth [2], a low-energy sliding phonon mode is built in. We report on recent transport studies at up to ~120 kbar in antimony, which assumes a similar structure. (ii) We have used high pressure quantum oscillation measurements [3] to track the electronic Fermi surface and carrier mass in the correlated metallic state of the pressure-metallized Mott insulator NiS2 up to ~120 kbar. Our results show that the Fermi surface changes little but the quasiparticle effective mass increases strongly on approaching Mott localization. (iii) The ruthenate Mott insulator Ca2RuO4 metallises at moderate hydrostatic pressure and undergoes further structural changes with increasing pressure. Band ferromagnetism is observed over a wide pressure range, but its signature fades out above about 80 kbar. Instead, we confirm an earlier report of superconductivity [4] below about 0.2 K and find a new anomaly at elevated temperatures which suggests a spin density wave transition.

[1] Goh, S. K. et al. Phys. Rev. Lett. 114, 097002 (2015)
[2] Brown, P. et al. Science Advances 4, eaao4793 (2018)
[3] Semeniuk, K. et al. arXiv:2202.04024 (2022)
[4] Alireza, P. et al, J. Phys.: Condens. Matter 22, 052202 (2010)