Regensburg 2013 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 38: Correlated Electrons: Metal-Insulator Transition 1

TT 38.12: Vortrag

Mittwoch, 13. März 2013, 12:30–12:45, H20

Optical Investigations of the Metal-Insulator Transition in κ-(BEDT-TTF)₂Hg(SCN)₂Br — •Tomislav Ivek^1,2, Rebecca Beyer¹, Rimma N. Lyubovskaya³, and Martin Dressel¹ — ¹1. Physikalisches Institut, Universität Stuttgart, Germany — ²Institut za fiziku, Zagreb, Croatia — ³Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Russian Federation

Due to its fundamental character as well as the promise of practical applications, multiferroicity is at the forefront of investigations in solid state physics. Out of many candidate materials there has been a recent increase of interest in the κ-(BEDT-TTF)₂CuX family of quasi-2D organic conductors due to the pronounced dielectric response found in the magnetically-ordered phase. Puzzlingly, in these compounds the infrared vibrational spectroscopy and NMR do not find the charge disproportionation which is a basic prerequisite for electric dipoles.

On the other hand, a related but still unexplored set of mercury-based materials, κ-(BEDT-TTF)₂Hg(SCN)₂Cl,Br, shows evidence of charge disproportionation at low temperatures. We present a detailed investigation of the κ-(BEDT-TTF)₂Hg(SCN)₂Br using infrared spectroscopy and dc transport. Below the metal-insulator transition at 80 K a small transport gap of 20 meV is found within the conducting molecular planes. Far- and mid-infrared spectra are taken between 300 K and 8 K along the three crystallographic axes. We discuss the common optical features as well as more exotic ones compared to the Cu-based κ-materials, particularly temperature dependence of the charge-sensitive vibrational mode ν₂₇(B1u), in light of recent theoretical descriptions.