Molecular solids Model systems for exploring interacting electrons in reduced dimensions

Prof.dr. M. Lang
J.W. Goethe-University, Frankfurt (Main), FOR 412, Germany

Solids, made up of extended molecular units containing stable p-radicals, provide flexible building-block systems for exploring the interplay between strong electron-electron and electron-phonon interactions in reduced dimensions. Of particular interest are the quasi-2d charge-transfer salts k-(ET)2Cu[N(CN)2]Z (Z = Br, Cl) and l-(BETS)2Fe1-xGaxCl4, where transitions between different symmetry-broken states such as insulating, antiferromagnetically ordered, metallic and superconducting can be induced by small variations of chemical (substitution) or physical (pressure, temperature or magnetic field) parameters.

Likewise, magnetic insulators based on open-shell transition metal ions interconnected by suitable organic linkers provide ideal model systems for studying quantum magnetism in reduced dimensions. In particular, by using bridging ligands which mediate an exchange coupling of moderate strength, these low-dimensional spin systems can be studied in the interesting intermediate and high-field region, i.e. across the saturation field gmBBs = 2J.

In this talk, examples from both classes of molecule-based materials with strong electron correlations will be discussed. Particular emphasis is placed on the anomalous metallic state and its interrelation with superconductivity for the k-(ET)2X compounds and acoustic anomalies near the saturation field Bs as a generic property of the antiferromagnetic S = 1/2 Heisenberg chain studied on a new Cu2+ coordination polymer.