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Anomalous Lattice Response at the Mott Transition in a Quasi-2D Organic Conductor

M. de Souza·A. Bruehl·Ch. Strack·B. Wolf·D. Schweitzer·M. Lang
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Abstract

Discontinuous changes of the lattice parameters at the Mott metal-insulator transition are detected by high-resolution dilatometry on deuterated crystals of the layered organic conductor $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br. The uniaxial expansivities uncover a striking and unexpected anisotropy, notably a zero-effect along the in-plane c-axis along which the electronic interactions are relatively strong. A huge thermal expansion anomaly is observed near the end-point of the first-order transition line enabling to explore the critical behavior with very high sensitivity. The analysis yields critical fluctuations with an exponent $\tildeα \simeq$ 0.8 $\pm$ 0.15 at odds with the novel criticality recently proposed for these materials [Kagawa \textit{et al.}, Nature \textbf{436}, 534 (2005)]. Our data suggest an intricate role of the lattice degrees of freedom in the Mott transition for the present materials.

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M. de Souza, A. Bruehl, Ch. Strack, B. Wolf, D. Schweitzer, M. Lang. 2007-12-11. Anomalous Lattice Response at the Mott Transition in a Quasi-2D Organic Conductor. https://doi.org/10.1103/physrevlett.99.037003

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