Physik
Fachbereich 13

The Mott metal-insulator transition, a paradigm of strong electron-electron correlations, has been considered as the source of intriguing phenomena. Despite its importance for a wide range of materials, fundamental aspects of the transition such as its universal properties are still under debate. In a recent publication, we report detailed measurements of relative length changes as a function of continuously controlled helium-gas pressure for the organic conductor k-(BEDT-TTF)₂Cu[N(CN)₂]Cl across the pressure-induced Mott transition. We observe a breakdown of Hooke’s law of elasticity in a wide range of temperature and pressure around the Mott critical endpoint. We assign these non-linear strain-stress relations to an intimate, non-perturbative coupling of the critical electronic system to the lattice degrees of freedom. Our results are fully consistent with mean-field criticality, predicted for electrons in a compressible lattice with finite shear modulus. We argue that the Mott transition for all systems amenable to pressure tuning shows the universal properties of an isostructural solid-solid transition.

Science Advances 2, e1601646 (2016)