Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 46: Low-Dimensional Systems: Molecular Conductors

TT 46.2: Talk

Tuesday, April 1, 2014, 14:15–14:30, HSZ 204

The Search for Massless Dirac Fermions — •Rebecca Beyer¹, Armin Dengl¹, Tomislav Ivek^1,2, and Martin Dressel¹ — ¹1. Physikalisches Institut, Universität Stuttgart, Germany — ²Institut za fiziku, P.O. Box 304, HR-10001 Zagreb, Croatia

The quasi-two dimensional organic conductor α-(BEDT-TTF)₂I₃ is a semimetal at high temperature and low pressure. At T_MI = 136 K (ambient pressure) it undergoes a metal-insulator transition and becomes charge ordered. Pressure is known to reduce the transition temperature and theory predicts a Zero-Gap-Semiconducting (ZGS) state once the transition is fully suppressed. This ZGS state was thoroughly investigated in terms of Landau Levels: many different experiments prove the existence of a zero-energy Landau-Level at high pressures (p > 15 kbar) and low temperatures (T < 10 K). Only few studies comment on the evolution of the ZGS and the linear dispersion relation in the band structure with pressure or temperature. For example first principle band structure calculations predict a Dirac cone even at room temperature and ambient pressure but with a finite chemical potential.
We present infrared reflectivity measurements under intermediate hydrostatic pressures (0 < p < 10 kbar) on α-(BEDT-TTF)₂I₃ between room temperature and 10 K. We show the evolution of the insulating gap and investigate the possible coexistence of massless and normal charge carriers in one of the few bulk materials with a ZGS state.