Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 26: Metal-Insulator Transition

TT 26.5: Vortrag

Donnerstag, 29. März 2007, 15:00–15:15, H19

Lattice response at the Mott Transition in a Quasi-2D Organic Conductor — •Mariano de Souza¹, Andreas Brühl¹, Christian Strack¹, Bernd Wolf¹, Dieter Schweitzer², and Michael Lang¹ — ¹Physikalisches Institut, J. W. Goethe-Universität, Frankfurt am Main — ²3. Physikalisches Institut, Universität Stuttgart, Stuttgart

The Mott transition, which is the metal-insulator (MI) transition driven by electron-electron interactions, is one of the key topics of research in the field of strongly correlated electron systems. Deuterated salts of the organic κ-(BEDT-TTF)₂Cu[N(CN)₂]Br charge-transfer salts, here BEDT-TTF (or simply ET) denotes the donor molecule bis(ethylenedithio)tetrathiafulvalene and X a monovalent anion, have been recently discussed in this context. In this contribution we report on the direct observation of the lattice response through the Mott transition in the above-mentioned compound. Discontinuous changes of the lattice parameters at the Mott transition are detected by high-resolution dilatometry experiments. The uniaxial expansivities uncover a striking and unexpected anisotropy. A second-order phase transition is observed near the end-point of the first-order transition line T_MI. The extraordinarily large lattice response there provides a sensitive thermodynamic probe to explore the critical behavior. The analysis yields a singular contribution with a critical exponent α=0.6∼0.9 and indicates the particular role of inhomogeneities giving rise to a broadening of the transition.