The stress-strain relationship of Sr2RuO4 across a Lifshitz transition.*

The stress-strain relationship is a standard characterisation of engineering materials, but not of quantum materials. This is chiefly because of challenges in measurement: typical samples of quantum materials are small, and large strains are typically required to achieve interesting changes in electronic structure. Here, we report stress-strain data on Sr2RuO4 as it is tuned through a stress-driven Lifshitz transition. At 4 K, the Young's modulus of Sr2RuO4 drops by ≈10% at the Lifshitz transition, then increases by ≈20% beyond it, solely due to changes in electronic structure. Most of this change can be accounted for with a non-interacting model. We also show that stress-strain data can be used to obtain the condensation energy of a stress-induced magnetic phase in Sr2RuO4 that occurs beyond this Lifshitz transition. These results show that stress-strain is a promising technique for obtaining thermodynamic data on electronic phase transitions in quantum materials.