Eur. Phys. J. B 56, 285-290 (2007)
https://doi.org/10.1140/epjb/e2007-00121-8

Metal-insulator transition in the low-dimensional organic conductor (TMTSF)₂FSO₃ probed by infrared microspectroscopy

¹ Experimentalphysik II, Universität Augsburg, 86159 Augsburg, Germany
² Institute for Synchrotron Radiation, P.O. Box 3640, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany
³ Department of Physics, Ewha Womans University, Seoul, 120-750, South Korea

Corresponding authors: ^a oleksiy.pashkin@physik.uni-augsburg.de - ^b christine.kuntscher@physik.uni-augsburg.de

Received: 19 December 2007
Revised: 3 April 2007
Published online: 11 May 2007

Abstract

We present measurements of the infrared response of the quasi-one-dimensional organic conductor (TMTSF)₂FSO₃ along (E) and perpendicular (E) to the stacking axis as a function of temperature. Above the metal-insulator transition related to the anion ordering the optical conductivity spectra show a Drude-like response. Below the transition an energy gap of about 1500 cm^-1 (185 meV) opens, leading to the corresponding charge transfer band in the optical conductivity spectra. The analysis of the infrared-active vibrations gives evidence for the long-range crystal structure modulation below the transition temperature and for the short-range order fluctuations of the lattice modulation above the transition temperature. We also report about a new infrared mode at around 710 cm-1 with a peculiar temperature behavior, which has so far not been observed in any other (TMTSF)₂X salt showing a metal-insulator transition. A qualitative model based on the coupling between the TMTSF molecule vibration and the reorientation of electrical dipole moment of the FSO₃ anion is proposed, in order to explain the anomalous behavior of this new mode.