It is common procedure to measure the stress-strain relationship of engineering materials, but much less so for correlated electron materials. Reasons that this is a challenging measurement for correlated electron materials include the difficult mechanical properties of many electronically interesting materials, the need for low temperatures, and the need for strains of order 1% to observe interesting electronic effects. In this talk, I will tell you about the stress-strain relationship of the correlated metal Sr₂RuO₄. Compression along the [100] lattice direction drives the largest Fermi surface through a Lifshitz transition, from an electron-like to an open geometry. We find that the Young’s modulus has a sharp dip at this transition, by about 10% of its zero-stress value. This large effect can be explained mostly by band structure effects alone. Beyond the Lifshitz transition, the Young’s modulus rises by more than expected. I will also show Hall effect data, that indicate a pronounced change in electron-electron scattering across the Lifshitz transition.

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