Giant lattice softening at a Lifshitz transition in Sr <sub>2</sub> RuO <sub>4</sub>
Hilary Noad, Kousuke Ishida, Y.-S. Li, Elena Gati, V. Stangier, Naoki Kikugawa, D. A. Sokolov, M. Nicklas, Bongjae Kim, I. I. Mazin, Markus Garst, Jörg Schmalian, A. P. Mackenzie, Clifford W. Hicks
Abstract
The interplay of electronic and structural degrees of freedom in solids is a topic of intense research. More than 60 years ago, Lifshitz discussed a counterintuitive possibility: lattice softening driven by conduction electrons at topological Fermi surface transitions. The effect that he predicted, however, was small and has not been convincingly observed. Using a piezo-based uniaxial pressure cell to tune the ultraclean metal strontium ruthenate while measuring the stress-strain relationship, we reveal a huge softening of the Young's modulus at a Lifshitz transition of a two-dimensional Fermi surface and show that it is indeed driven entirely by the conduction electrons of the relevant energy band.