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 Ivek^1,3, and Martin Dressel¹ — ¹1. 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 T_MI = 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.