In this talk I will discuss recent angle resolved photoemission (ARPES) experiments on Ca2RuO4 under uniaxial strain. External tuning parameters such as magnetic fields, pressure and strain play a key role in the study of quantum materials [1]. Yet combining them with direct measurements of the electronic structure by ARPES proved challenging.
Using ultrathin plate-like crystals mounted on a bending-type strain apparatus, we recently succeeded in driving the archetypal multiband Mott system Ca2RuO4 across the metal-insulator transition, while monitoring the evolution of its electronic structure by ARPES [2]. Our measurements show that metallicity emerges from a marked redistribution of charge within the Ru t2g shell, accompanied by a sudden collapse of the spectral weight in the lower Hubbard band and the emergence of a well-defined Fermi surface. In the metallic state, we find a substantial enhancement of the spin-orbit interaction over its atomic value. I will briefly discuss the relevance of these findings for other correlated systems as well as new opportunities opened by combining quasi-continuous strain-tuning with direct electronic structure measurements.

References
[1] C. Hicks et al., Science 355, eaaf9398 (2017)
[2] S. Riccò et al. arXiv:1803.00488 (2018)