Dresden 2011 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 48: CE: Metal-Insulator Transition 2

TT 48.2: Talk

Thursday, March 17, 2011, 10:45–11:00, HSZ 105

Localization-delocalization transition in the κ-(ET)₂X salts: Evidence from fluctuation spectroscopy — •Jens Brandenburg¹, Jens Müller¹, and John A. Schlueter² — ¹Johann Wolfgang Goethe-Universität, Frankfurt am Main — ²Argonne National Laboratory, Argonne, IL, USA

Quasi-2D organic conductors κ-(ET)₂X with X = Cu[N(CN)₂]Cl, Cu[N(CN)₂]Br and Cu(NCS)₂ are model systems for low-dimensional metals exhibiting both strong electron-electron and electron-phonon interactions. The interplay of charge, spin, and lattice degrees of freedom lead to a variety of different magnetic-insulating, metallic, and superconducting ground states. The normal-conducting state shows anomalous behavior at a temperature scale T^∗ ∼ 35 − 50 K interpreted, e.g., as a crossover from coherent to incoherent transport.
Fluctuation spectroscopy is a new powerful tool to study the intrinsic charge-carrier dynamics in these materials [1,2]. Systematic investigations of four compounds, situated at different positions in the generalized phase diagram, show clear signatures in the temperature dependence of the relative noise amplitude a_R = S_R · f/R² at T^∗ depending on the correlation strength characterized by the ratio of bandwidth to on-site Coulomb interaction W/U_eff. This indicates a localization-delocalization transition in the interlayer transport on the metallic side of the phase diagram as a function of temperature or electronic correlation strength. Funded by SFB/TR 49
PRB 79 (2009), 214521
PRL 102 (2009), 047004