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Regensburg 2013 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 58: Poster Session Transport & Matter at Low Temperature

TT 58.39: Poster

Thursday, March 14, 2013, 15:00–19:00, Poster D

Zero-Gap State in Organic Conductors — •Rebecca Beyer1, Armin Dengl1, Mohamed Assili2, Tomislav Ivek1,3, and Martin Dressel111. Physikalisches Institut, Universität Stuttgart, Germany — 2University of Tunis, Tunisia — 3Institut za fiziku, Zagreb, Croatia

The quasi-two-dimensional molecular crystal α-(BEDT-TTF)2I3 exhibits a metallic behavior down to TMI = 135 K, at which it undergoes a metal-insulator transition into a charge-ordered state. This transition is very sensitive to hydrostatic pressure: it not only decreases the transition temperature by about 9 K/kbar but also the charge disproportionation gets reduced with increasing pressure. Above a certain pressure of about 15 kbar, the metal-insulator transition is completely suppressed and the material goes into a zero-gap semiconducting (ZGS) state with close similarities to the Dirac-Cone in Graphene. The ZGS-state has been predicted by theory and been supported by dc- and Hall-measurements while the NMR-response shows very exotic features which also have been assigned to ZGS fingerprints.

For further investigation of the ZGS state in α-(BEDT-TTF)2I3 we performed infrared optical measurements in the frequency range of 100 cm−1 to 8000 cm−1 at temperatures as low as 10 K under hydrostatic pressure up to 15 kbar. We were able to follow the decrease of the transition temperature and the closure of the insulating gap with increasing pressure. Calculations were performed predicting the optical conductivity of free charge carriers in a tilted Dirac-Cone, in order to compare experimental results with theory.

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