Berlin 2005 – scientific programme
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TT: Tiefe Temperaturen
TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique
TT 16.8: Poster
Saturday, March 5, 2005, 11:00–16:30, Poster TU C
Influence of electronic correlations on the Drude response of two-dimensional organic conductors — •Natalia Drichko1, Martin Dressel1, Jaime Merino2, and John Schlueter3 — 11. Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany — 2Universidad Autonoma de Madrid, Madrid, Spain — 3Materials Science Division, Argonne National Laboratory, Argonne, USA
We use organic conductors as model objects to investigate the effects of reduced dimensions and electronic correlations. Conductivity in BEDT-TTF crystals occurs in the planes of the organic molecules, the overlap of the molecular orbitals defines the bandwidth W, the electronic correlations depend on the BEDT-TTF molecule parameters.
For the compounds α-(BEDT-TTF)2MHg(SCN)4 (M=Rb, Tl, K, and NH4) the structural parameters vary slightly, leading to an increase of ratio of electron-electron correlations to W on going from metallic Rb-salt to Tl, to K, and further to NH4 (which becomes superconducting at Tc ∼ 1 K). By measuring polarized reflection in the conducting plane of the crystals in the 8000-50 cm−1 range from T=300 K to 5 K, we investigate how the electronic parameters depend on temperature and electronic correlations. The intensity of a Drude-peak increases below 50 K. The width of the Drude-component decreases when going from the Rb to the NH4-compound, which we relate to the increase of electronic correlations. In addition, in the K-salt a pseudogap is observed around 100 cm−1 at T below 50 K, indicating charge-order fluctuations close to the superconducting state.