Research ArticleCONDENSED MATTER PHYSICS

Breakdown of Hooke’s law of elasticity at the Mott critical endpoint in an organic conductor

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Science Advances  07 Dec 2016:
Vol. 2, no. 12, e1601646
DOI: 10.1126/sciadv.1601646

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Abstract

The Mott metal-insulator transition, a paradigm of strong electron-electron correlations, has been considered as a 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. We report detailed measurements of relative length changes ΔL/L as a function of continuously controlled helium-gas pressure P for the organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl across the pressure-induced Mott transition. We observe strongly nonlinear variations of ΔL/L with pressure around the Mott critical endpoint, highlighting a breakdown of Hooke’s law of elasticity. We assign these nonlinear strain-stress relations to an intimate, nonperturbative 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 moduli. We argue that the Mott transition for all systems that are amenable to pressure tuning shows the universal properties of an isostructural solid-solid transition.

Keywords
  • Strongly correlated electron systems
  • Mott metal-insulator transiton
  • critical phenomena
  • thermodynamic studies
  • thermal expansion
  • organic charge-transfer salts
  • effects of hydrostatic pressure
  • coupling of electrons to lattice degrees of freedom

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