Regensburg 2016 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 78: Correlated Electrons: Poster Session

TT 78.32: Poster

Donnerstag, 10. März 2016, 15:00–18:30, Poster D

Optical investigations of disorder in spin liquids — •Miriam Sanz Alonso — 1.Physikalisches Institut, Stuttgart, Deutschland

Quantum spin liquids (QSL) emerge from frustrated spins on a triangular lattice with anitferromagnetic interaction. As proposed by Anderson, frustration prevents long range magnetic order down to lowest temperatures. In his model the ground state consists of resonating valence bonds (RVB) and is therefore highly degenerate. One of the most investigated QSL materials is the organic compound κ-(BEDT-TTF)₂Cu₂(CN)₃ which is a two-dimensional Mott insulator with triangular lattice. As it was also observed for closely related charge transfer salts, charge fluctuations may play a key role for the physical properties. Until now, this material was subject to magnetic, thermodynamic, transport and also some optical studies, supporting the proposed spin liquid behaviour. Recently, dielectric measurements observed typical fingerprints of relaxor ferroelectricity. Thus, we performed comprehensive spectroscopic investigations in the mid-infrared to track the temperature dependence of a charge-sensitive molecular vibration. As a result, sizeable charge disproportionation between the BEDT-TTF sites can be ruled out. In addition, we observed similar behavior in the closely-related compound κ-(BEDT-TTF)₂Ag₂(CN)₃. To examine the influence of disorder on the ground state, parameters like the cooling rate and chemical composition of the donor layer were varied.